Well that got a bit ugly for a moment... Since it is up there, and I am actually a newish player myself I will give my 2 bits on CSGs. I can see the allure. They add a depth to the game in strategy. By making you do things you might never have wanted to do. Depending on what you like they can be both fun, and !FUN!. You have to solve this extra puzzle and it gives the strategist types something more to play with. However I can see the downsides as well. It is HARD railroading. And a lot of people CAN NOT STAND THAT. Railroading, even landholding style hard type, can be useful. And when well done can be rather unobtrusive. But the CSGs are NOT well done. They were, from what I have gathered, a reaction from the original developer to ultra-low AIP games deep-striking the AI HWs without ever being threatened by the AI in a real way. In short, Chris went "Stop breaking my game you bastards! It's pissing me off!" and threw deliberate roadblocks to prevent it. Harsh words maybe, but from the looks of it, probably true. They were tossed in without any kind of testing or discussion, and are rather clunky and ill designed IMO
Now personally, I don't like them. I tend to play on the "bull**** maps", if I recall the phrase correctly, and sometimes the only way to get to a portion of the galaxy, for things I might very well need, is to go THROUGH a AI HW. Trust me, the AIP gain (but now it is AIP Floor gain so maybe not so bad now) from neutering the place is MUCH preferable to having core posts in your way that you CANT deal with. But part of what makes this game SOOO good is the fact that despite not being "Mod Friendly", it can be VERY adaptable. There are ways to make the game to conform to what you want it to be, within reason. You can have the same game appeal to both groups, and as well it is very hard to have the exact same game twice, even when trying.
Now, on to economy and crystal. I agree that crystal is a rather weak mechanic right now, but I also think that simply removing conversion between M & C and rebalancing the economy around that is NOT the right move. I build the big things, starships, golems, spirecraft, and FS. And while there are no hard numbers right now, just going from what I have read, and guessed at, this is going to make doing that a bit harder on me. I play at 300% to AVOID economy issues and any PSP/PS2 time (I don't have netflix, too broke) while I wait for things to (re)build. I want the fun (and the !FUN!) to start fast and stay going for as long as possible. (Which is funny because I'm actually kinda a slow player, still learning higher level strats)
Personally I think removing crystal entirely is a better idea. The split is mostly 50/50 on the majority of things, and when it is not is also mostly arbitrary. One would think that all the alien stuff, most especially Spire anything, would be 70% or more crystal, while Human based tech runs 70% or more metal. Why are starships so different from fleetships rule of near 50/50, if they are supposed to function similarly to them, but with less DPS and more HP? The splits that are not nearly 50/50 rarely make sense for any given reason I can think of. And for the ones where it is nearly at or at 50/50, the split has no meaning. There is no added depth at all.
Final bit. While I am sure the current idea you have would be easier to code, perhaps another way to factor the Simple Economy toggle could be used. Rather than just merging them together and getting needlessly large numbers, do the following. Use ( M + C ) / 2 for all costs. Add them together, and then divide that result by 2. All income sources that produce both M and C do so in equal amounts, so you can just drop C out of them and would still be just as effective. For harvesters, divide their income by 2. Since the number of them has not changed, and all of them are now just metal, your income shouldn't change either. As you now have 2x the number of metal harvesters, you can get by with 1/2 the income from them. This would keep the numbers on costs from getting too pointlessly high (especially on high cost items like golems, trader toys, and FS) while at the same time give a new starting point from which to balance the cost of things from.
After all that, you could work out something NEW to use crystal for. Because while the idea of making Metal and Crystal work similar to something like Starcraft Minerals and Gas (where low tech things only cost minerals, and as the tech level goes up things cost more and more gas) sounds like a good idea on paper, I don't personally feel that it works for core game. Right now the key costs of higher and better tech are
A} Resources. Higher marks cost more of BOTH M+C. Bigger things cost even more so, but it is both M+C is nearly every case. And as stated, most things are nearly 50/50 or have a split that makes no sense to have. Meaning, IMO, you could get rid of either M or C and still have the same costs.
B} Knowledge. You need to pay K costs for the vast majority of tech improvements. And given that in most cases the things that don't just give you free power also give the AI more ways to kill you, you still need to spend K to survive long enough to keep/acquire the better toys.
C} Energy. This is your supply cap. Not as strong as the raw ship caps, but not ignorable either unless you have more planets, (which costs either AIP or having extra HWs) or you have an economy that can support multiple converters without breaking. Which means you spent a lot of K on it or have a lot of planets.
Given the 3 things above, do we really need to add/change it to have crystal work like gas? Starcraft has an entirely different econ system that it is designed around. I see no reason to take a working system (crystal may be removable but it still works) and turn it into something else entirely. You would need to do a LOT more rebalancing to get that to work than if you just removed C from the equation. Because you still have the A from above, in the form of M. You could allow C to be worked into new and more interesting things, and even have C worked into certain minor factions like Golems. Maybe they don't self attrition but rather cost so much crystal to get up and running again but can NOT be repaired unless you have that much crystal income/sources/ect. Spirecraft also need to be looked at, and crystal could be integrated into them as well. Still takes full asteroids to build them, but now costs crystal rather than metal to repair/build any of them. You would also likely need to give crystal some way to work in the core game as well, without options, but I am out of ideas for that right now.
COMPLETELY OFF TOPIC IGNORE THE STUFF BELOW IF YOU DESIRE
I normally don't talk much about the balance of the game economy wise, since, as I have said before, I out right cheat. 300% Economy and a starting K of 250k. But in this case, I felt a little compelled to say something. This is after all a major change, and even for me it will have a big impact on how I play and what I do. On the cheat issue, more than a few times I have thought to make an AAR about my games, but always refrained from doing so for the simple grounds that I am cheating. Would there be any thing against the rules about posting one? And if not, would anyone even care? Or, as I have feared, would the reactions be "Meh, you're a cheater so I am going to either ignore you or criticize you for not playing fairly" ?