Well I guess I shouldnt feel as bad about driving my TTA on a daily basis anymore since it is only one of the other 1324 cars (T-Tops and leather) and now has over 40,xxx miles on the odometer.
The way I see it is that I'm not planning to sell it and I can't take it with me so what does it really matter what it is worth. I want to get the most enjoyment out of it as I can and can only do that by driving it. If I had bought it as an investment (which is really stupid to do for nearly any car) I would have bought one with only a couple thousand miles on it, not 34,xxx.
As for modding it, go for it, especially if you save the original parts or th stock parts just give out. Tubbing out a low mileage good shape GNX would be crazy though.