Actually, I think Matter Converters are a problem. Currently, I don't really need to make any choices with regards to energy. Since I can trade M+C for Energy, and since I have effectively infinite time, I can trade M+C income down to very low levels and support max cap of everything I have. It takes forever to rebuild, but for maximum power I'm encouraged to do that.
Since CPAs have a minimum effective AIP that increases with time, you don't have infinite time, but perhaps it's not steep enough that you're worried about it in your scenarios.
Worse, I can micro a refleet by destroying a chunk of Matter Converters to up my refleet speed until I hit my energy ceiling.
That's not ideal, no, but at least you'd be somewhat more vulnerable to brownouts during that time. Though perhaps not by much.
Another observation is each planet produces K Knowledge. On average each point of Knowledge unlocks something that requires X Energy to support. Each Energy Collector produces E Energy. If E / K > X then Energy is largely pointless. If E / K < X then Knowledge is largely pointless. Basically, Knowledge and Energy are currently the same. You get a fixed amount of each per planet (ignore Matter Converters because they just make Energy completely irrelevant).
There's something to that, but:
1) K, once spent, cannot be redirected. E can.
2) Not all units have the same K/power and E/power ratios. Fortresses are notable for this.
3) Running out of K can leave you without flexibility. Running out of E can leave you dead.
4) A lot of units come with no K cost (mkI triangle and initial bonus type, most mkI starships and turrets, spirecraft, golems, some FS ships, post-nebula faction ships, etc) and rely on E for "population balance".
@chemical_art on the AI power curve vs the human power curve, and @Valtiel on the benefit-received-per-planet: I think both those perspectives are looking at it the wrong way. From a "I want to win" perspective there's only one question you need to ask to determine whether you want to take another planet: "Do I need to take another planet to be able to kill the AI Home Command Stations?". Correct me if I'm wrong, but I think there's absolutely no other in-game reason (i.e. not "because it's fun", that's valid but it doesn't bear directly on balance) to take a planet or do anything else that causes AIP. Well, aside from "Do I need to take another planet to keep the AI from killing my Home Command Station?", but that seems to be a rarer thing and as has been pointed out generally taking another planet isn't going to give a net positive on your defensive situation, and if it consistently
did then you could just take all the planets.
So the point isn't how much you get from taking another planet, or how much the AI gets if you take another planet, the point is whether you need more to win. Whether it's because the CSGs are on and you literally
need to take those planets to be able to attack the AI HCSs, or because Lazy-AI is off and you effectively need more K or E or whatever to have any realistic chance at taking down the AI HCS defenses before it kills you, or whatever.
If you don't have what you need to take down the HCSs, then you need more planets (or something; hacking or superweapons or whatever). Doesn't matter how much you'd gain from the planet or how much the AI would (if the AI would gain more such that you'd be further from winning, you've probably simply lost).
If you
do have what you need to take down the HCSs (including position), then there's no reason to take more planets. Doesn't matter how much you'd gain from the planet or how much the AI would.