I know Agrav fields are apparently ubiquitous in the present-day sector, so that one definitely won't need them.
There's also the consideration that Agrav fields may be less effective when they have to operate in a gravity well. Whatever the lore justification for why it works or doesn't, if you decide to do it could you also add an option to add Artefact demand to structures that you don't think should have the demand by default? Perhaps for Domed Cities too? I like to make all the terraforming/environmental mitigation solutions hard to obtain (or at least seem hard to obtain), and having something more than a big price tag/upkeep helps there.
I agree that the terraforming structures should feel hard to obtain or have some sort of special requirements, but it's difficult to do that in a way that both makes sense lore-wise and also creates fun gameplay. Requiring DAE for all terraforming buildings doesn't make sense lore-wise since some of them can be built using real life 21st century technology, and others are clearly viable with sector-level technology.
I could go the route of requiring special items that can only be found through salvage, but that dilutes the loot pool and many players don't want to have to explore the entire sector every time they start a new save just to terraform.
I tried locking certain things behind quests that had to be completed in a previous version of the mod. That worked OK, but the new story quests in 0.95a are very lengthy and high quality, and mine weren't quite up to that standard. Plus, it takes an enormous amount of time to create quests, especially if they have branching outcomes.
Finally, I have to consider that most players aren't going to play the same save for dozens of cycles. If terraforming takes too long or is too expensive, they'll never get to use it.