Personally I think you're freakin' nuts!!! JK
Enjoy the car and stop worrying! Losing $5k would be nuts IMHO, and if you are that worried use $1500 and buy an extended warranty. Not to mention, if you buy the S2000 and lose the $5k you will also lose the looks and performance of the Boxster. Frankly, it's worth the small chance of a major engine failure to save $5k and drive the Boxster.