I'm interested in collecting the best players and the rarest cards, so anything that is highly valued for some other reason seems overpriced to me. And there are plenty of literally unique cards, so the fact that I could pick up
this one for under $200 while others that I'd really like to own, such as
this one cannot be had for under $100,000 does make the latter (equally rare as a specific set/player combo, much more common as a type, even if you specify the California League) seem a bit odd. Maybe if Jennings had sharper corners...
The other thing I'd say in general is that wherever there's a discrepancy between how great a player was and how popular he is to collect, that seems almost by definition to be an overvaluing of the cards. That's true even for some of the greatest players in the game's history. For instance, I'd have Mathewson, Gehrig, and Mantle each ranked among the top 25 players in MLB history (but outside of the top 10), whereas the prices their cards command suggest they're all among the top 10 players. Eddie Collins by contrast, also one of the top 25 players, seems undervalued. Not to say that buying Collins or selling Mathewson is a brilliant financial move right now, but if there's much value in cards 100 years from now I suppose I'd bet that Eddie Collins would rank a bit higher and Mathewson a bit lower than where they are right now.