Hi there, i noticed no one has replied so I thought I would.
Firstly i don't know anything about this particular car itself so this is in general, however these cars can be expensive to maintain, at under 2k miles a year on average has it been serviced well? has it been run regularly? has the air con been used regularly? i'd imagine at 2k miles a year the air con is barely on.
These cars can have a few mechanical and electrical gremlins however there is alot of knowledge available on them, a few specialists in the US who can often get parts that Porsche dealerships in the UK cannot.
With auto's they can suffer from TBF this can grind the engine block down inside and write it off so you must have the car up on a ramp to check for this, especially spending that much money. This PDF file show what damage can occur and what it takes to check it. http://members.rennlist.com/v1uhoh/928TechFlexPlatearticleTH.pdf
Mine is an early car so it took about 15min to check it. If you have cats then the exhaust may need to be moved.
You don't mention if the car is an S4, GT or GTS etc, this can make a difference to its value.
forums.rennlist.com are useful as is the 928.org email list at http://www.928.org.uk/mailman/listinfo/928uk
If you have any questions the email list can be very helpful.
HTH