There is an old saying with Porsche... If you have to ask, you can't afford it.
thstone and I have been on a very similar path. Instead of dropping a wad on the car, we invested in the driver. Our expenses have been pretty similar although I spent very little on the car for the first 5 years of ownership. Only last year did I crack the piggy bank a bit with fully developed suspension, trans, clutch, IMS retrofit, waterpump, Tstat. Pretty normal stuff with 100k miles and 60+ track days I guess.
The Boxster is still the most fun car I have ever owned and I will continue to push it's performance envelope at the track as often as possible.