Seriously, they're really bad. Why are they so bad? Please fix them.
Average planet yields 4 Raw Production. (1 Base + 3 Population)
Space Elevator costs 20 and yields 1 +0.5/Level All Construction.
Deep Core Mine costs 32 and yields 2 +0.3/Level Social Construction.
Starport costs 38 and yields 2 +0.5/Level Ship Construction.
Factory costs 50 and gives 5% +1%/Level All Construction.
Computer Core costs 24 and yields 1 +0.5/Level Research.
Galactic Mainframe costs 90 and yields 1 +0.5/Level Research.
Xeno Laboratory costs 100 and yields 5% +1%/Level Research.
Central Bank costs 64 and yields 1 +1/Level Gross Income.
Market Center costs 50 and yields 5% +1%.Level Gross Income.
Xeno Farm costs 30 and yields 1 +0.5/Level Food.
City costs 67 and 4 Food and yields 3 +0.5/Level Population.
Space Elevator, Deep Core Mine, and Starport are decent, but aren't needed on every planet. Factory is just bad, even with ideal adjacency.
Computer Core is sometimes useful, but Galactic Mainframe and Xeno Laboratory are just bad.
Central Bank and Market Center are trash.
Xeno Farm and City are the only improvements worth building all the time