The latest Porsches aren't like that, typically. That 2010, for example, has the new engine generation, which addressed a most of the problems in that department, at least if you stay off the track with it. Water pumps are still weak, but a real bargain at only $800 for a new one, installed.
The PDK is an iffy proposition off-warranty, but the six-speed is pretty solid. The real issue is whether or not you can do your own maintenance, like oil changes, brake pads, and air filters; it'll save a bundle every year if you can. That is one nice thing about audio systems, they never need a nine-quart synthetic oil change, and they don't have water pumps.
Regardless, get a Cayman S. It's worth the risk.