[Mydis]

If defending a base, and not continual counter-attacks, is not a valid tactic, I promise trying to make it one will not be fun.

I do agree with SpaceDrake, that an artificial system like gaining extra exp would not be a good idea. It would have to be something more natural, like making bases much easier to defend, which could be handled in several different ways: more automated turrets, more range of turret types, like AA and AP. Structure of the base gives defender the upper hand(cover, slowing large vehicles with obstacles, bunker type windows, etc), or maybe the best idea would be to lessen the number of bases. Fewer bases might make things more organized, less constant scrambling about, and lead to larger, more epic battles.