Take a few moments and a good floor jack and work light and get under that car, you might not even need a PPI, on the pre-gal cars the BIG issue is RUST.
If you see substantial RUST under the car I would pass and not even bother with the PPI.
You can always repaint the car you have to a color you like, 12K invested in your current car can get alot done,
Just my .03
Todd
Porsche's are like a box of chocolate, you never know what you are going to get until you take a bite...