Sounds like you are doing everything right. I don't mind as much because them moving a little stops the bars from bending. The rubber bushings keep out alot of vibration too, but some guys solid mount their bars. The loosen it up, staighten, tighten down-method should be all you can really do. New bushings should have helped. What about the metal cap washers? are they smashed inside out?
I opted for solid bark busters. They save the bars, levers, perches, front brake, throttle, and cables. They keep your fingers from getting smashed by limbs, trees or crashes. They also keep the bars from really digging into the ground. I haven't broke or bent anything on the bars since installing them......
If you don't wreck, you're probably not riding hard enough