Well early in the season I bought 3 Tony Parker SPX rookies for $9.99 each they are now selling in the $40+ range. Even all of the Tim Duncan autographs have taken a nice jump (unfortunate is more like it). I haven't tracked Duncan rookies but i have with his autographs.
I think that the Spurs have an exciting team. Guys like Ginobili and Parker are very exciting. I think the biggest problem is that they lack USA super hyped players and fans don't really go for boring but efficent players like Duncan.
Everyone recognizes Duncans talent and every team would love to have him. However outside of the Spurs fans very few people collect Duncan cards. They are more interested in going for guys like Vince Carter, T-Mac etc.