Didn't porsche change the cpo plan in 2008? IIRC, PCA changed the cpo warranty to be an extension of the original bumper-bumper warranty, whereas before there where many items it excluded. This would account for the large increase in price I would think.

I remember my dealer telling me it costs about $2500 or so to register the my car as cpo, not including any service/work needed. But he could have been lying (imagine that).

I'd negotiate the price of the car as a whole. Times are still tough and these cars are moving themselves. Plus you're coming into the best time of the year to negotiate buying a car.