For some reason, I wasn't aware Merc had made a V8 version of the R172 SLK (the 2011-on model). It doesn't look quite as good as the R171 like Matt's old one, but it does have 414bhp and must surely be worth keeping an eye on as prices fall.
I enjoyed mine for what it was. The R172 has more power, much better gearbox (with rev matching!) and optional diff as well - the latter of which I felt was the biggest issue with mine, so I imagine it's a much better car to drive.
The downside, is the looks. Exhausts aside, it doesn't stand out against the rest of the range at all. They're still £25k+ as well, and considering you can get an R171 for £8k these days....