Correct me if I'm misunderstanding you but it seems that you're trying to bring BALANCE to Aurora and that's not going to work 
Truer words are rarely spoken.
In my view there are two kinds of balance. One is I think what most people think of which is to make every option for everything equally viable in a futile quest to eliminate any and all One True Answer scenarios, which is not only an impossible pursuit but tends to make games feel very overbalanced and bland.
The other, better kind of balance is one which tries to create a useful role for all elements of the gameplay even if some of those roles are relatively niche. This is a much more achievable goal in practice because it really only requires Steve to make everything usable, not powerful. However this does still require some work in some cases, but on the whole I think this is the kind of balance Aurora strives for much to the chagrin perhaps of many players.
In the case of terraformers, I think the core issue is that right now ground-based 'formers are only usable in the technical sense - you can build them and they function - and once 10k RP has been invested into the 'former module and tractor beam techs, ground facilities are inferior in every way except for generating tax money. Primarily this is because they cost 600 BP while orbital 'formers only cost 500 BP a pop, plus a bit more for structural materials and crew quarters.
It is I think important to separate this point from the others. Yes, ground 'formers have a lot of limitations such as requiring population to operate or more shipping capacity to move around.
These things are perfectly fine. However, the fact that they are significantly more expensive to construct is a serious problem - while "there will never be a situation where you want less terraforming ability", I will virtually always prefer to spend 500 BP than 600 BP to get the same effective terraforming ability.
Even if that's not the case and there's a mathematical most efficient way, it doesn't really matter. Because Aurora is all about options and possibilities - if TF facilities are only useful in early game and then might not be used by few/some/many players after that, doesn't mean that they are wasted. It's 100% fine if something isn't viable/efficient throughout the game - we already have this with weapons. There is no need to make any changes here.
I think there is a little bit of a difference between "mathematically most efficient way" and "one way is almost strictly worse than the other AND more expensive by 20% to boot".
I think comparing to ship weapons actually supports the point here. For example, plasma carronades are, let's be honest, generally a third-tier weapon system at best in terms of performance, however they are very cheap to research (partially due to changes made in C# to bring balance!) and still have niche uses such as JP defense and ground unit attack boosting. Early in the game plasma can be a very strong weapon, but later on while it does drop off it retains some good uses. Now if plasma carronades cost more than, say, particle lances(!) we would have a serious balance problem, building plasma ships would be not merely suboptimal but in fact a cripplingly bad decision. Similarly, 10cm railguns are excellent point defense in the early game, while Gauss eventually pulls up even after ~20k+ RPs and only becomes clearly superior for PD after another ~50k RPs. However the railguns remain quite useful even if they are not as good as pure PD due to cheapness of BP and RP as well as being better for volume of anti-ship fire in a close brawl, plus they are better for beam PD fighters due to relatively small size. Basically my point is that while different weapons are more or less powerful in different game eras they all remain viable even in niche roles, no weapon is completely eclipsed by another in nearly every way.
Point being, while it is fine for something to be viable early and then drop off I think it is preferable for that something to be at least worth using in some sense throughout the game if possible, and I support the need to make a change where this can be accomplished without undue work... changing the ground terraforming facilities from even 600 BP to 500 BP I think falls under this category. Orbital modules will still be generally superior but ground facilities can still present a case to be built even after those 10k RP have been spent and a tug fleet constructed.
E: To be clear, I do think all this talk about halving the cost, quintupling the efficiency, or removing the population requirement is several bridges too far. I just don't think a simple adjustment to bring the costs into line between the two options is a bad idea, in fact I think it is a good one.
