I collected sports cards like any kids during my tween and teen years. I still have many of them (lots of commons, plenty of marquee players too) tucked away in a closet, as the idea with sports cards was that they'd appreciate in value as time went by. I was told by a card shop owner that I was probably paying for college by purchasing (and keeping preserved) the cards I was buying, because cards were being sold at incredible prices at the time.
Yet overproduction of sports cards basically killed the industry. Unless you have a special insert card and the gimmick it contains (a signature, a piece of game-worn jersey) or you've had your card "graded" to show how pristine the condition is, the card is worth next to nothing. Oh, sure, there are times certain player cards will be worth more than they had been (winning an award, traded to another team, signing in another market, retirement, hall of fame induction) but for the most part - cards seem to lack all value right now.
Case in point: Former Tampa Bay Lightning right wing and current New York Rangers forward Martin St. Louis The March 5th trade from the Bolts to the Rags alone should have increased the value of his cards - at least in times gone by - and his current status as a key contributor (offensively and dramatically) for the Rangers in the playoffs should also inflate prices for his card offerings; especially his rookie card. The 1998-1999 Upper Deck card (#234) features Marty in his Calgary Flames playing days, long before he found success and acclaim in Tampa Bay.
Becket price guides used to be the barometer for the value of a sports card. At this point in time, you have to be a member of their web site (and I don't know if that includes paying anything to subscribe). As a casual collector, seeing what the market is paying for cards is much easier by just going to eBay and seeing prices that people are asking / paying for cards.
In the instance of Marty, the going rate stands at less than a dollar. "Buy It Now" prices are under $4. Compare that to P.K. Subban's cards - mostly gimmick insert cards. Yes, Subban is a young star in the league, which props him up. St. Louis? Future hall of famer, two time Hart Trophy nominee and 2004 winner, among other accolades to his name.
Perhaps the card was a common in the 1998-99 Upper Deck series, which will deflate the card's value... It's still been almost 16 years since that set of cards was printed and sold to the public in the US and Canada. While player relevance increases the value of cards, or should, time is also a factor as the number of cards in circulation decreases with each passing year. Cards get lost, damaged, thrown out and generally destroyed by various means.
It used to be like the stock market, at least for baseball cards, with rates fluctuating for reasons already listed as well as overall player performance. I figure the same was true with hockey cards (which I collected much fewer of). In either case, the sports-card collecting craze seems to have run its course. Cards seem to be a novelty now, not much more.