I thought humans need more encouragement to attack, not to defend ?
How about this: humans get no money for killing if a turret deals the killing blow. It would certainly encourage humans to come out, without touching the stats of turrets and teslas.
Not that the fence doesn't look pretty, but tremulous is designed as aliens-are-melee-only game. It would be too hard to take down with only stage3 adv. dragoon able to shoot. Now try taking down the fence with melee aliens... I'm sure players would soon find a lot of abusive places where laser generators can't be seen, not to mention touched.. Aliens don't have grenades or splash damage.
And if you make it deal too low damage, then what's the point of it ?