First, since I'm relatively new here (again), note that I generally play on 7/7 and consider myself an okay, but not fantastic player. Also note that I've only had about 30-40 hours worth of experience with the 6.0+ version of the game (the last version I played being circa 2009).
I must also note that I'm used to playing with a bit higher AIP than seems to be norm (at least on the forums) these days. 400-600 used to be the recommended (And I think the wiki still recommends this), but if you aren't working on the second homeworld at 400-450, I don't think you have much longer to live anymore. I don't know if the base game without expansions enabled is a point of balance anymore , but I would like to note that at ~400 AIP you get into a stalemate situation with the AI based on pure fleet/starship attrition and income rates. Without super weapons and no fallen spire I am relying entirely on a wide array of MkIV ships and core fabs to do all the heavy lifting on offense and defense. You end up right now in 'economic stalemate', where if you clear out the released threat you need to partially refleet, by the time that is done, the threat has built back up. Attempting aggressive actions is very difficult because as soon as you leave with a large enough force to make a dent in the front line the threat starts to pour in back home. You'll often lose your offensive force in achieving the objective, while getting attrition ed on defense, forcing more wait time while you refleet 6 caps of mark IV's. (having fooled around a bit with expansions at this point, I'd also like to note that expansion bonus ships in general seem to be slightly more powerful/more diverse than the original game ships, which are mostly dps/force multipliers of some type and are built to either soak damage or provide larger amounts of dps, dying in large numbers in the process.)
This, needless to say gets very dragged out as auto-AIP ticks. Higher AIP used to be very grindy without being in danger of dying (unwinnable situations). Now it outright kills you when you don't have the resources to refleet/rebuild fast enough. It kills me at lower AIPs that I would have expected though. A weaker economy will only exasperate this. Nerfing the overall economy will make higher AIP (and by 'higher' I mean 400-500, the low end of what is supposeds to be 'acceptable' at the endgame) to play without superweapons. This may be intended, as 'vanilla' games where you have to play fleeter or starshiper without any toys enabled may not be a balance point anymore.
It sounds like very 'low planet' strategies are running a bit high on economy right now, but 'higher AIP' empires (superweapons or not) still need the higher-octane economies to support them. I'm actually doing much better in my most recent attempt, where I've done two things: (1) turned auto aip off (I really don't want to turn autoaip off again though) and (2) kept my AI progress much lower (only capped 15 worlds total, with 8 data centers and the homeworld I only 'paid' for 6 of them in effect: 120-140 AIP total only). This has lead to much more success, but also means that I don't actually need an economy because my stuff simply doesn't die because the AI never has enough of anything anywhere.
I think the low-economy effect happens to be a sub-issue of low-AIP type games. in anything above 300 AIP, you really, really need the resources that the current harvesters generate for refleeting (well, if you aren’t using supeweapons anyway). I'd strongly urge if you do something to nerf the economy you try to avoid hurting higher AIP games that need the resources badly.
If harvesters are mostly a problem in Low AIP/no planets taken games, here are a few possible solutions:
1) I think the easiest and simplest solution is to reduce the number of harvesters on the human homeworlds (note: I'd leave the harvester numbers on the AI homeworlds alone, it's a nice bonus if you can hold onto it). You can also perhaps slightly increase the average nodes found per planet (maybe by just one, or one every 2 or 3 planets) to encourage taking of more planets to help balance it out; it'd probably net out as a slight increase to larger empires.
2a) If harvester efficiency is reduced in some way [say marks are removed or nerfed, as was suggested above], I think higher AIP games needs to have some way to make this up. Perhaps something like raising the cap on the number of MK II and MK III econ stations that can be built.
2b) Still assuming harvester efficiency is reduce in some way, another possible solution would be to have some kind of global increase, depending on the total number of planets/harvesters you have. This would maybe be an addition to the econ station; increases economic output of harvesters (or maybe even global economic output?) by n%/2n% per MkII/MkIII station. This would allow larger empires to keep up during the attrition wars while reducing early game/low planet economy. This has the added benefit of synergizing econ stations with harvesters, making someone who spent the full 18k knowledge (I think that's how much it costs?) have a super-economy. That's the same knowledge cost as 3 MkIII unlocks, if I'm not mistaken.
3) This next one is really complex, but another potential option is to change the role of MkII and MkIII harvesters to be more useful for larger empires, and econ cmd stations to be more useful for smaller empires.
I'd accomplish this by having MkII/MkIII harvesters generate the same resources as a MkI harvester, but it each harvester would be boosted by a percentage per same harvester controlled globally (I’d suggest you keep the %’s separate for metal and crystal). This would cause large resource boosts (I'd try to balance it to roughly where MkIII's are today for a 15-20 planet player). This would also scale human players economies up at larger sizes, where I feel that they are at disadvantage sooner to where they used to be (well, superweapons non-withstanding of course.) Also, this makes each 'harvester kill' and Cmd station kill the AI does in a high AIP/higher human world game more detrimental: you need to hold onto your territory effectively and prevent harvester deaths to retain higher economic bonuses.
Let's work out some numbers, I checked a few games I had: 14 planets controlled had 64 harvesters (4.6 harv/planet), 18 planets controlled had 78 harvesters (4.33 harv/planet). If we want to use the 18 planet game as the balancing point: mk II harvesters produce 30, or 1.5 times that of a Mk I and MK III harvesters currently produce 55, or 2.75 times that of a Mk I.
With that in mind, 100 harvesters (I'd estimate that'd be ~25 planets): MkII should remain a 50% boost; if the 100 harvesters are split evenly [they are unlikely to be, but assume for this], then 50 metal harvesters should each give a 1% bonus to total metal generated from harvesters, totaling a 50% boost (150% total harvester income). Same would apply to the crystal harvesters.
MkIIIs ghould remain a 175% boost; if 100 harvesters, then 50 metal harvesters should each give a 3.5% bonus to total metal generated per harvester.
The bonuses would be smaller for few-world games, and larger for many-world games. You can change the point where you want the balance to be with some quick calculations, but the net effect is that higher mark harvesters benefit larger, higher AIP games where the resources are needed more. Thus these upgrades mean your economy no longer scale linearly. there are a few things to keep in mind about this:
* REALLY high planet capture rates will give the player a HUGE economy. I still don't expect it to keep up with growing AI waves, growing boarder aggression, and higher Mk ships in general though, unless the player somehow manages to become super cost efficient (which is possible with superweapons I suppose; I don’t really have the experience with them to comment).
* 'economic spiral of doom' is easier to achieve, as killing 3 or 4 planets will scale your economy down by twofold: loss of resources from the harvesters themselves and loss of multiplier on all other harvesters.
4) This is a variation on the previous idea (but is probably too computationally intensive to implement). rather than a global bonus, which can potentially have tricky out-of-control scaling (though I think the AI still scales even FASTER), give a bonus based upon # of total harvesters built only on adjacent planets. This will have a number of effects:
i) Benefits more contiguous empires; leaves economic command stations for more spread out empires.
ii) affects map balance: maps with more adjacency (think cross-hatch) will have higher bonuses, allowing players to better keep up economically with the additional avenues of attack.
iii) scales up with more planets, but doesn't scale out of control due to the 'local' restriction.
iv) buffs play of more contiguous empires or ‘clusters’ of human worlds (this may or may not be desirable).
5) In the context of resources, you can globally reduce the amount of m/c (and maybe energy too) produced, but then have excess energy flow into either 'energy->metal' or 'energy->crystal' converters. Balance it so that a target planet size (n) comes out about the same. This makes losing command stations (and energy collectors hurt more). This will slow down low-planet games economies bit while still allowing for decent resource flows at higher AIP games. This also allows you to rebuild/refleet faster if everything you had just kicked the bucket, but it slows down as you approach cap, since your energy is no longer channeling into crystal/metal production.
Or you can combine any number of these changes... but balancing that might be a bit of a challenge.
Lastly, if a global economy nerf is in order, I'd suggest seriously looking at the threat release mechanic. I seem to be losing a slow war of attrition at ~400-420 AIP... maybe I'm just not that good.
I don't have much to say about energy. Energy now acts as a global food cap for all units/buildings/etc, since it does not divert resources anymore. If the intent is to just leave it as a global food cap, then it probably needs some tweaking (that is, the energy per planet should probably come down, but perhaps the bonus to the homeworld should be buffed so you can still produce quite a bit off of 1 world?) You simply either have enough energy or you don't.
I’m not sure how you can re-introduce energy having an opportunity cost without allowing energy micro back into the picture. Perhaps just a global reduction of energy per planet is in order? I don’t seem to ever be short energy in my higher AIP games, unless I’ve lost half of my worlds, at which point I should be dead by all means anyway.