I had a ton of money in my last 911 ('73T/RSR). When I sold it I just showed the guy the phonebook thick folder of parts receipts. I gave him copies of the ones he wanted and through in a few tech books as well. Some of the work was farmed out, those receipts were kept as well. Generally, your time and work is worth nothing and the parts are worth about 1/2 when you go to sell the car. It looks pretty impressive to have those high dollar bills for labor, but you sure won't come out ahead for it. When I do general maintenance on my cars I log the work/mileage/date/notes in a logbook created for that purpose. This is about all you can show a potential buyer. They will be able to tell that you are an enthusiast who keeps his cars nice.
