Build and expand with structures on the surfaces of planets, given that you have sufficient power, fuel, metals etc. That might give the game a bit more meaning, and insentivise expansion. For example, you start with a simple launch pad and VAB on starting planet. Find minerals to harvest, and build power generators. Launch satellites to find more resources. Then launch to asteroids or moons to harvest minerals and fuel on those. I would love that.
PS: might also require some extra "prospecting and construction" camera mode, where for example the cam can move along the surface of a body the ship has landed on within a certain distance, to select areas for new structures to be built.