I agree that turrets seem a little useless at later levels. What if turrets dealt consecutively increasing damage? What I mean is that every consecutive tower shot a champion takes deals 10% increased damage or something like that. (This consecutivity would be lost if the turret is no longer targeting a certain champion). This wouldn't affect turret hugging much, because going in for pokes will end up with the same result, but will punish sustained diving, because the longer you stay under there, the more damage the tower shots will do. Just a thought.