While you're checking the ball joints and bushings, inspect the rims to see if any are bent. In recent years I've seen a huge increase in the number of bent wheels. The C/CLK chassis are pretty good on ball joints so I doubt you'll find any problems there. We do a fair amount of control arm bushings, but not because of ride quality issues, we just find them starting to crack during routine maintenance. Also, the brand of tires can make a huge difference in ride quality.