IMHO, Combat doesn't need to be rebalanced it needs to be rethought. I don't like running around in circles around a base while shooting it up and getting chased any more than planting down some turrets and watching the carnage. For me and I think many other players right now combat is a chore. Its main problem is that it is static. Playing with damage levels and ranges will never make it less static it will only change what you shoot and where you stand while shooting.
With a sufficiently developed ai I think the aliens as they are now could pose an interesting challenge. It would be great if the aliens "learned" from the player and adapted.
- They could change where they attack after too many die in the same place.
They could attack in greater numbers.
Probe your defenses at multiple places at the same time.
Make it so behemoths go in first to draw laser fire.
When a behemoth is adjacent to the wall allow smaller biters to climb over it to get over the wall.
Make spitters focus fire.
Spitters could shoot walls in front of turrets to open the way for biters without coming to harm.
Berserk small biters that ignore target priority (crazy little shits that go after power poles, belts or anything else in sight)