^ I agree, a warranty is something to seriously consider in older Boxsters that have not passed 30k miles, because they are more prone to engine failure. But if you absolutely have to have the car and it doesn't have a warranty, just get a good PPI, and then watch carefully. You can spot RMS and other problems a head of time if you are observant. Like oil dripping as a precursor to RMS.
I purchased an 8 year old, 17k mile garage queen, and the main thing to look at are the seals. If the car just sat around for a long time, the fuel lines, etc. will dry up and have stuff crystalize in them. That is why I got a warranty to 54k miles. Once you pass 30k you are normally safe with a Boxster, and after-market warranties are not to expensive, mine has already saved me $5k.
Just y $0.02!