First biggest improvement to Starbases is the implementation of Request Constructor Button. Good job there. I wanted this exact thing when I was playing Galciv2.
Second biggest improvement to Starbases. Have them actually fire their weapons at attacking enemies while there's allied fleet defending it. Aka participate in the combat not sit on their asses and watch cartoons while there's a battle raging. This would require the starbases to have different weapon range capabilities from ships but hey, I'm sure everyone will understand. Especially after they watch a starbase sit there and do nothing while enemy murders 6+ scout ships stationed on a starbase and then proceed to shoot at starbase and have starbase wake up and start shooting back. This entirely destroys the purpose of having a "castle" in space. Ships cannot find refuge in it. Other than being allowed to field a single bigger fleet than usual through 60 logistics points.
Third biggest improvement to Starbases. Having more than 200 hp. Gaining hp with each module installed would be great.
Fourth biggest improvement to Starbases. Military Starbases need to be scary to attack. I somehow expect a fully upgraded Military starbase by endgame to go all deathstar on a lone random battleship. That's probably just me though. I do expect Culture and Economic, and mining starbases to be weaker than Military starbases in battles. Because duh, space is taken up by embassies/markets/barracks for miners that would have been used for armor + guns.
And where's my big red button on military starbase? I wanna blow it up if I can't have it to take down that offending battleship who is soloing it easily and deny the enemy the satisfaction of destroying it.