Maybe each major planet can have room for one "military research facility," a structure that increases an attribute to all space units galaxy wide.
Only buildable on planets like Coruscant, kuat, fondor, byss, bastion, etc... MAJOR world
Since only one per major world you would have to choose
-Sublight drive research facility (5% speed boost)
-Weapons research facility (5% weapons power boost)
-Shield technologies facility (5% shield boost)
-Power generator development facility (small rate of fire, shield recharge rate, and speed boost)