17 inch wheels? That will have a huge affect on ride quality and noise. If you want "like-new" ride quality, you need "like-new" wheels, which are 15 inchers with, I think, 65 series sidewalls.
That said, I'm pretty dissappointed with the noise and rough ride quality of my w124 that I recently purchased. The tire selection will also make a difference. Do some research on quiet tires on in the wheels section for some ideas.
'84 300D, 173k
'90 300CE, 163k