I spent quite a long time debating between the Cayman R and the M3. The M3 is practical, comfortable, powerful and has an amazing engine. The Cayman has sublime handling dynamics and the feeling that the car pivots around your hips.
After driving both back-to-back the difference in power was very striking. Honestly, the Cayman didn't feel much (if any) faster than my E34 M5 in a straight line. I felt like the Cayman needed about 50-60 more hp. That said, if I wasn't looking for a DD and just wanted a weekend/track toy, I'd seriously consider a Cayman R based on handling alone.
I think a Boxter Spyder would be a fantastic car to have in SoCal. You might miss those extra horses, though. I know I would.