I really did get lucky on my 98 Boxster, I guess. I'm the 8th owner
I did't get a PPI and relied on some paper work from the last owner that indicated IMS replacement at 30K, I'm at 72K at purchase. The parts that need replaced are because they are simply old. Regular maintenance was done but not much else.
What I've learned.
A PPI will give you a lot of assurance about what the future might hold for repairs. You'll find all the obvious issues. My door locks were foo bar, and I didn't even notice till I got home, god I'm such a nube!!! I'm about $1000 into maintenance for just old parts. Not bad, but I can do the work. If there's no record of IMS then it's not been done. The
Durametric abuse info will be useful and the cam deviations will be useful. I would expect a PPI to provide that info.
You might just want to plan about $3k for repairs for a mystery machine. Just decide to do the clutch IMS and RMS, Oil change, AOS and some hoses, Water Pump; and from what I know so far that prevents the most serious and costly issues.
If you aren't sure about these issues then step up to a certified pre owned model.
My personal philosophy related to cars, either make enough $$ to have someone work on it or learn how to do it your self, and have something else to drive in the mean time.