Buildable stations

I think a few different station types would add more for every playstyle.

There could be habitat stations orbiting planets in a system, operating similarly to moons, adding a population slot to the planet. This could be done maybe 1-2 times depending on planet size. These habitats would be built from a new button next to terraforming and planetary improvements. So if a player already knows they are aiming for a tall playstyle, they'll focus even more on finding big systems to terraform into better planets and filling habitats in orbit.

There could also be somekind of starbases as a system improvement, and they could also have a starbase design section under ship designs. They probably wont need a starbase cap per system, as long as their upkeep is kept high. Maybe starbases upkeep is very high to low depending on the upgrades it has, so bigger and stronger require a lot more to maintain and if a wide empire wants a few bolstering starbases here and there, they could just build a bit smaller ones? In combat these starbases would always influence the fight from the background, and if the defending fleet is defeated or there is none anyways, the aggressor fleet has to engage the starbase, somewhat similiar to Vodyani Arks.

Somekind of economic stations would be great aswell, maybe if your system has influence over or connected by a starlane to a Collapsing Star, Black Hole, Nebular Clouds and so on, the station would boost up the yields more.

And for scum influence players like myself, somekind of broadcast propaganda station to boost influence of a system drastically to convert nearby systems. It could be something like, the more neighbouring systems you have nearby maybe up to 4 starlane jumps away, your system's influence is boosted with 80%/(1.25^x-1) and the x is number of neighbouring systems so if there is only 1 neigbhouring system, it's a 80% boost to influence and for 2 systems it's 80%/(1.25^2-1)=64% bonus per system which means 128% bonus of influence if there is 2 systems nearby and so on.

The same type of scaling could also be used for the economic stations, with different numbers though, providing bonus FIDSI on the system depending what systems there are nearby.

Filling the different stations into science tree wouldn't be hard either, Science and Exploration has the habitat station, Empire Developement has the influence station, Military has starbases, Economy and Trade has the economic stations. Starbases in techstage 2 and other stations at techstage 3 in their respectable trees. And to be clear habitats are planetary improvements and other stations would be system improvements.