In my mind, (a scary place at times
) you need to be honest with yourself and your abilities. Can you change the alternator yourself? If you can, then that issue is any easy fix. The same can be said of most repairs that this car needs, or will need in the next year. Most people can't or won't do the IMSB swap themselves understandably. Can you afford that repair and the clutch, RMS, motor mount, while your in there repairs that go with it?
$11500 sounds high-ish to me for the SoCal market. What's the $$ number in your mind that makes this a no-brainer?
I know you are wisely trying to be careful in your selection. I am concerned that you are taking the joy of these cars ownership out in the process. Some of these cars explode, despite our best efforts and intentions. If that is going to haunt you, you won't be able to fully enjoy what these cars have to offer.
Let them sit on it awhile. The market for a Porsche that needs an alternator on day one of ownership can't be very large. Especially after the first snows start falling. Make sure they have your number and tell them to give you a call when they are more reasonable? Good luck in your search.