Are you familiar with Bricklink.com? If you're able to identify a set or piece through there, you can look at their price guide to see pricing histories and averages over the past few months. Very handy imo.
Personally I'd be very interested in buying some things from the 2001 - 2002 era, but there seems to be a discrepancy between my idea of a "fair price" and what the "going rate" seems to be right now. Still, if you ever have trouble identifying some of those early sets, I'd enjoy trying to help identify them.