Your vibration at highway speeds is surely a tire balance problem.
The dealers use Hunter GSP 9700 balance machines, and they can take care of the problem, unless that is, your tires have too much wheel force variation.
Check out their website for a good description of what that means and how that machine can balance tires that no other machine can handle:
www.gsp9700.com
One thing to always remember is that you have chrome wheels. With chrome wheels, you can only use the stick-on weights on the underside of the wheels. You cannot achieve a perfect balance using these weights because you are only applying weights to one plane. At freeway speeds above 65 mph, you may get a slight tire vibration.
With other wheel types, you can use the clamp-on weights. This way, you attach the weights to the outside and inside lip of the wheels. You are applying weights on two planes, and thus achieving a dynamic balance. BTW, the clamp-on weights that Mercedes uses are unique to Mercedes wheels and will not put a scratch on Mercedes wheels.
I have traveled overseas quite a bit on my job, and have noticed that chrome wheels are a uniquely American thing. You will not find chrome wheels in any other country.
Just my $.02 cents (and with another $0.99 you can buy a cup of coffee).