Personally, I think Starbases are too puny. MUCH too puny. I can upgrade a Starbase with tons of weaponry and defense, and it still will die quite easily to all but the most puny attack fleets. I usually have to park a fleet of my own on top of my Star Bases to prevent the enemy from destroying them. The only thing Starbase attack components seem to do is deter the AI from destroying your starbases with a Scout armed with a Laser. In End-Game situations, a fully upgraded Starbase is more vulnerable than most of my painfully un-upgraded ships.
Maybe it's just me, but I think Starbases should be more powerful. Plus, I think the amount of constructor ships required to fully arm a Starbase is ridiculous. Of course, one shouldn't be able to build the DEATH STAR with just a handful of constructors, but spending a dozen constructors for a Starbase that can barely defend itself doesn't really seem worth it.
I also dream of Starbases taking part in tactical battles with ships in the same square as they are.