I think part of the logic behind the spawn points is this...
First if GVs were allowed to spawn at the enemy base, then why not planes?
Second, part of the "reality" portion of AH is that planes and/or GVs need to navigate to their intended targets. Thus allowing for combat not directly related to defending a base.
Just as with planes, GVs can and do encounter defenses along their way. Whether that's an opponent hiding in trees, underpasses, camping at the spawn point or directly defending the intended target.
I think the distances needed to be traveled are a good compromise. Otherwise, you'd be driving for hours from your original base and camping out overnight for long campaigns.
Tank towns were more or less in response to a minority group wanting a place to build perk points. IMHO, they are useless and unrelated to the overall object of the game. They provide no value to winning a map and do nothing but eat up resources on all sides.
