This game has the potential of promoting team play and objective-oriented play quite easily. However, the most effective way to play currently is to farm grunts as much as you can in order to outlevel your opponent. Immediately aiming for your opponent's base is generally suicidal, not necessarily due to an inability to successfully take out enemy structures, but purely because you earn no XP/Gold by doing so.
Grunt killing should be a peripheral task to trying to penetrate your enemy base. Forcing people to farm grunts to stay competitive focuses on one of the duller elements of the game. Since it is the most effective way to compete, it also forces people to play this way, rather than opening the game to more creative tactics.
If I kill a few grunts while pushing up to my enemy's base and manage to down a tower, why shouldn't I receive XP and Gold? Why should a person 1-2 shotting npc's (something that your AI towers will do) end up with better award stats (dmg/level/gold and due to this more than likely pvp superiority awards) for farming such creatures?