Why not make it a backwards system lowering valor rewards based on either node control or population. I don't know if anyone has said this(lots of pages >.<) but I know for a fact thats its alot harder to encourage people to go out and save people from spawn campers when they won't get as much as the imperials will for the fight. If you make it so imperials get **** rewards while camping the flightmaster of that base then they'll leave and republic will start moving in. Republic takes some bases and imps come back wreck **** and leave.
Other than that a queue for it with minimal grouping could work try to even both sides and spread em out over the entire map. For overpopulated servers you could even have imp on imp illum maps i know you guys have already created the system for creating multiple maps.
Another thought make it so the turrets dying will spawn something really nasty, raid boss maybe could drop awesome loot, could drop terrible loot doesn't really matter just something to tip the scales so the spawn camping stops.
Maybe give the republic an out of the way gy when the republic base is destroyed sure you can't fly out of the place but at least your not in a *****torm of aoe that kills you immediately. I'm a republic guy and though i honestly have not been to illum yet(terrified to after a youtube video) I do think its a really cool concept though it might be 100% impossible to implement.
I absolutely think however that you have to be able to give a player a safe place to respawn and if necessary a way to get out of a place. Without those two things i would never ever go to illum might as well delete my character.