I have a general car question, its not about my Integra but about my Mercedes. Maybe one of you guys can answer it. Here goes!

Ok, while driving at any speed above 80MPH my 98 C43 shakes/vibrates too much. I'd like to know why? Its not even fun or safe feeling to be going over 80 for more than a few seconds. I feel I have no control over the car.

Is it wheel balancing? (did it about 8k miles ago or 14-16 months ago)
Shocks? (the car has Brabus lowering springs for 16K miles now)
Tires? They are match set but are about done on tread wear.
Something else????

I figure its time to spend some $$ on it and fix the problem. So please help