Am I spending too much on my boxster?

[BoxsterSteve]

Store it if you want, but starting it periodically is a bad idea. The engine needs to get up to operating temperature, and that takes 15-20 minutes of driving. Idling just doesn't cut it.
Do like most and don't run it while in hibernation. Your car will thank you.
Fill the tank, add some fuel stabilizer, pump up the tires and throw a cover on it.

As far as what you have spent, it's all preventative work and setting a maintenance baseline.
Don't fret.