And a couple other things I'm thinking about but am considerably more hesitant about:
6) Quarter the effectiveness and the K-cost of the harvester upgrades (so you still get the same boost per K, but it "maxes out" much lower).
7) Double the number of metal and crystal spots seeded by mapgen on non-homeworld planets (with some provision for old saves).
I'm actually of the opinion that Mk III harvesters are OP regardless.
I agree with this. My first point was that this isn't the only thing, knowledge efficiency is also part of it. But I do agree that the Mk. III (and to a lesser extent Mk. II) need to be toned down some, along with a knowledge efficiency nerf (which could just happen naturally if the K costs are unchanged but the higher marks receive a stat nerf).
My second point is that it doesn't have to be one or the other. Both "once built" stats AND knowledge costs could change to find a better balance.
Remember back in the ancient days of yore (last year, this time) when the complaint was that Harvesters were a waste, and the standard strategy for everyone was to grab three systems and drop Econ IIIs on them? And when the common consensus was that waiting around to rebuild was sooooooo boring?
Metal/Crystal Harvester II/III, in honor of getting 2nd place (by one vote) in the first "Worst Unit" poll in which they were eligible: A bit of background: Unlocking Econ Station II costs 4000 knowledge and gives a total of 576 m+c above the "standard" command station (econ I) if you build all 6, and that bonus is still relevant if you unlock Econ III. That's about 0.144 (m+c)/s per knowledge point.
Unlocking Econ Station III costs 5000 knowledge and gives a total of 1536 m+c above the "standard" command station. Benefit/K Ratio is about 0.3072.
Previously, unlocking mark II of either metal or crystal harvester cost 3250 knowledge and, assuming a mid-game situation of 13 total planets (i.e. all 6 of econ II and econ III could be placed) with an average of 2 spots of that resource per planet (ymmv, but it's probably not far off) gave a total of 208 resources above mkI harvesters. Benefit/K Ratio was about 0.064.
Previously, unlocking mark III of either harvester cost 4000 knowledge (but really 7250 since you don't get the benefits of mkII and mkIII at the same time like you do with econ stations) and, across 26 ressource spots, gave a total of 416 resources above mkI harvesters. Benefit/K Ratio (assuming 7250 "real" K cost) was about 0.0574.
So, to do something about this pretty vast disparity: Harvester II: Knowledge cost from 3250 => 2000.
Production from 28 => 31 (so +8 => +11).
Harvester III: Knowledge cost from 4000 => 2500 (so 4500 total).
Production from 36 => 73 (so +16 => +53). Yes, that's a lot, but that's what parity with econ III looks like. And nerfing econ III would have been an outrage considering how much waiting-for-resources happens on challenging games _with_ econ IIIs.
Yeah, the numbers for Harvesters at that time were 20/28/36. Currently they're 20/30/55.
Now they'd be 5/8/13? Even with double the resource nodes, we're looking at a 33%-50% nerf to where they were back then, when the community voted that the economy needed a serious buff.
Stop trying to nerf econ. If you have that much resources, you're sitting around too much. Go spend it. If all you're doing is doing Mark 1/2 of everything, that's your play style.
If you could win the game with MKI/II of everything on 9/9, and still have full resources, that would still be a balance problem.
Don't think you can, but in my experience I have plenty left over even after building everything possible with 0 knowledge on higher difficulties. I usually try to reactivate Golems at that point, but once you get 3 of those it just gets gratuitous 
I would love to have this excess resource problem you all have. Granted it's not as bad as it used to be, but I'm not sitting on max resources, ever. It just doesn't happen.
When using superweapons, I usually don't need to rebuild much. And that's the big difference right there.
As part of this discussion, I started a completely minimal game last week. All expansions, but no plots, no Champions, nothing. Diff 9/9. 3+ hours into this game, I have never hit more than the 200,000 resources I started with. I'm usually running at bare minimum. I spend 15-20 minutes out of each hour waiting for my fleet to rebuild.
I'm using Mk I/I Fighters, Mk I/II Bombers, Mk I Frigates, Mk I Attraction Drones in the fleetball.
When I can't fleetball, I'm using Mk I Spire, Zenith, and Bomber Starships (this requires a Matter Converter to support).
A fleetball rebuild requires 750,000 M+C.
A Starship rebuild requires 600,000 M+C. (F-in' Starship Dissassembers)
Supporting these ships requires a Matter Converter for an addition 200 M+C/sec.
I was lucky, with 13 resource nodes on my Homeworld (4/9, though - Conversion rates are hurting me badly). That's 520/670 per second income with my Harvester Mk IIs (the best I can afford so far) before the Matter Converter, 420/570 after.
757 seconds (12.5 min) to rebuild the Fleetball.
606 seconds (10 min) to rebuild those 4 Starships.
About 23 minutes to rebuild both. And either the Fleetball or the Starships (usually part of each) gets mostly wiped whenever I do something with it.
And you want to CUT my income?
My income would be 332/372 or so under the new numbers. That's adding another 10 minutes or more to my rebuild times. 30+ minutes, each time. And since I'm constantly doing stuff with this fleet, it dies a lot. So instead of 15-20 minutes of each hour being downtime, your suggestions would move it to 25-35 minutes.
Ok, fine. Solution is supposed to be "Capture more planets", which would give me more resource deposits. This is what this discussion is about, right? Making people do more than the bare minimum and gather some AIP.
So how much is the AI's response to AIP going to go down to match the requirement that I now need 40 additional AIP to get the economy to where I was before? Currently, that's 6 times as many ships per wave, a similar increase in Special Forces strength, and about a 125% increase in reinforcement strength.
