You can have both worlds. I'd say certainly drop the 4 motors. It's not necessary unless your primary purpose is to push. Cobalt was the perfect example of 2 motors and 2 wheels outdoing the competition, though, and that was down to good design. If the wheels are "in the middle" of the machine, à la Cobalt, I imagine you can also sort of fake the steadiness of 4WD through ESCs with breaking and/or a gyro. I can see that being worth pursuing if you still want to be ahead of most competition in terms of drive.