Re tops:
Got a couple of friends with SLKs....
One's a AMG with the 3.2 V6, the other is a SLK230 with the auto. The latter has mid 200k miles and has been a pretty reliable car overall. Both cars have a healthy appetite for tires, though.
Tops seem to be trouble free, with the caveat of hydraulic seals popping. Same issue with the SLs and W124 cabriolets. You can get rebuilt cylinders aftermarket for a pretty reasonable price.
Beware of any SLKs that have signs of rear end damage. That top is mighty fiddly, and if out of alignment due to damage, it can cause lots of heartaches.
The engine is a pretty reliable unit. We had that engine in our 00 C230 Kompressor. My brother has the car now, and it's got over 225k miles so far. Kompressors can and will fail eventually, ours was replaced when the car had high 100K something showing. Only downside is that it is kinda rough compared to other MB engines we've had. Sound rather agricultural.
I went to the dark side and have a BMW Z3. Kinda heretical, I know, but subjectively, Linda and I prefer the looks of the Z3. I much prefer the BMW six to the MB four as well. And the handling, the Z3 feels like a go cart compared to the SLK.
Something to consider though, is how small these cars are. Very little trunk space in either, and once inside, there NO room behind the seats. It's solid wall. Heck, even Linda's 68 MGB has tons of room compared to these new ones. Kinda sad when you have trouble getting a 6 pack cooler to fit inside your car....
Jim