My 2005 roadster just turned 45,000 miles - so far the only 2 things that have gone wrong
1. the drivers heated seat went -
2. 1 of the elements on the rear window defroster doesn't work

outside of that - car runs like a charm, I am not concerned that I will ahve issues coming at me with the car, there is too much mercedes in the car to start getting worried, the convert top is exactly like my 97 Audi cabriolet - that after 7 years of non stop up and down still worked flawlessly, If these are anywhere near Audi's quality - car has another 50,000 miles before I would even think to look for something to go wrong.
What you should look at is the tires - if they need to be replaced soon - you are out at least $700 to $1400 buck.

I intend to hang on to mine till I can't lower myself into it - so good hunting and hope to see you on the forum