One thing I would be a fan of would be increasing the range of a starbase to be roughly on par with a defensive platform, but making their weapons do less damage than current to compensate for the increased firing time. After all, the Sov has Type XII Phasers, and I believe those are "Starbase Class" weapons. When a tiny little platform has more range than an entire station which costs significant chunks of resources, something just seems a bit wrong.
To me, as they are, starbases are more like something to toss into a gravity well to try and prevent your planet from being lost by bombardment than a major tactical advantage. Sure they do lots of damage, but they can easily be avoided or their damage minimized, and if you avoid them you can attack the more vital structures like research/trade stations and resource asteroids which can severely cripple an enemy economy which is a major threat in itself.
I suppose if you cluster all of your buildings within the firing range of the starbase it might increase their overall effectiveness, but their range still makes that somewhat difficult. Even if you warp right into their firing range you can quickly move out of it before it can cripple your fleet, especially if you've upgraded to higher level tech.
Yes, killing a starbase that someone has spent a significant chunk of time and money on is a major kicker in the goal of conquest, but if it can't serve a major purpose as a defensive structure, it almost seems like a waste of resources, unless you're really keen on the delay it can cause by preventing loss from bombardment. To me, I just feel that a starbase should be something that, if you choose to invest your time and money on, it should give you back at least the equal cost in defensive ability.
Please understand that I am by no means saying that I hate the starbases in any way, just that I see a way they could be better and add more of a strategy to the game than they already present.