Throwing my two cents out there...
I don't think starbases should be able to move, and I think their range is just fine. The point of the starbase is not to singlehandedly stop fleets or keep people from moving through your system, or even keep them from taking the system from you while it is still there. The starbase exists primarily to HARDEN your existing defenses. It is the other defenses that should make the starbase difficult to ignore.
To use TEC as an example: If I'm dumb enough to build a starbase in a system with no fleet or tactical slot structure support, then a wily enemy ought to be able to knock out the system and then slowly whittle down the starbase at their leisure. Its my own fault for poorly positioning my defenses and for not adequately reinforcing the system. Frankly, if the enemy is able to move a significant number of ships through my border system, that says that i'm doing a bad job of defending myself. You get tons of advance warning from your jump scanners, you have the ability to dramatically slow jump drives in your system, you get to take potshots at them with fighters (even if they dodge your SB), you get to produce units in the time it takes them to fly through, etc.
On the other hand, if I build my starbase to face the primary approach lanes (from which I expect to be attacked) and then support it with 4 hangar bays, 2 or three repair bays, 4-8 gauss cannons, a phase inhibitor and a few frigate yards, then that is a force to be reckoned with. Even if the enemy moves around my defenses and attacks the planet from behind, they will only be able to bypass the close range weapons of the starbase itself. They will still be harried by long range fire and by my support strikecraft. More importantly, if I've built a planetary shield (near my starbase) and/or gotten the secondary government upgrade (for the starbase), I can minimize the enemy's ability to take the planet and/or strip control of the system from me. Even if they do take the planet, they will eventually have to engage my defenses directly if they want to get any use out of it. And, since I have frigate yards, I can be building reinforcements on site, buying time for my fleet to arrive. (I haven't even gotten into the use of minefields to steer enemy fleets towards your starbase by cutting off alternate routes).
Frankly, putting a starbase in a system on its own is a bit like putting an archery tower in a town when the Huns are coming to visit. You might as well just paint a bullseye on the damn thing and then grease it up for armor-piercing penetration. (the only exception to this is if you build one around a sun or asteriod field for the purpose of establishing a forward operations base. However, this should only be done with the expectation that you're going to have a fleet around to protect it/take advantage of it.) Archery towers and star bases can be extremely powerful tools, but only when used as part of a more comprehensive strategy.
No quantity of defenses can hold a system against a determined fleet. Properly designed defenses, however, should be able to tip the balance decisively to the defender in an otherwise fair fight. Furthermore, those defenses should be able to buy time for the defender (in the case of an unfair fight) so that they can marshall their forces. The starbases as they are do an admirable job of accomplishing that purpose. They aren't intended to be walls, or infinite bubbles of awesome, or permanent chokeholds. They are intended to be strategic strongpoints around which your forces can be rallied. If used intelligently, they can make it much more difficult for an enemy to hit your critical points (those systems and facilities that are essential for your victory) and make it easier for you to hit his. They can not, however, and should not, compensate for poor leadership in the field.