If you increase the range of Starbases anymore, they will be almost unassailable by anything other than carrier bomber fleets or the Vasari SB. You won't even be able to find a safe place in system to build a Vasari SB if the attack ranges are doubled.
As it stands, an intelligently placed Starbase can do a pretty good job protecting infrastructure around the planet and providing some cover at a chokepoint. If you build some PJI and other defenses near the SB along with hangars and hangar upgrades, you can make a pretty effective hardpoint.
Starbases just do not need to get any more powerful.... When you spend a lot of money on a starbase, it is to make it so unattractive to kill that people either have to fly around it or be willing to lose ships or 15 minutes to kill it. In my experience the assault cruisers are so vulnerable to strikecraft that they are almost useless to do their required job.
I have seen some clusters of defenses where the defending player has a Starbase, maybe an ally's starbase, and a maxed out defence grid with mines, PJI, and a small fleet hiding in there to provide additional support. You don't even dare fly past these chokepoints, because the positioning of the Starbase, PJI, and enemy cap ships guarantees you are going to lose a lot of ships trying to bypass it. Usually in these cases I have to resort to super weapons, because luckily the turtle has spent so much money on defense he is unable to attack me either.
Please think before you ask for starbases to be buffed further.....Entrenchment has already made the games much longer and more drawn out.