Last month, when my parents sold the house I grew up in, my mom forced me to come home and clear out my childhood bedroom. I opened the closet and found a box the size of a Jetta. It was so heavy that at first I thought it held my Weider dumbbells from middle school. Nope, this was my old stash. Thousands, if not tens of thousands, of baseball cards from the 1980s. Puckett, Henderson, Sandberg, Gwynn, and McGwire stared back at me with fresh faces. So long, old friends, I thought. It's time for me to cash in on these long-held investments. I started calling the lucky card dealers who would soon be bidding on my trove.

First, I got a couple of disconnected numbers for now-defunct card shops. Not a good sign. Then I finally reached a human. "Those cards aren't worth anything," he told me, declining to look at them...

Baseball cards peaked in popularity in the early 1990s. They've taken a long slide into irrelevance ever since, last year logging less than a quarter of the sales they did in 1991. Baseball card shops, once roughly 10,000 strong in the United States, have dwindled to about 1,700. A lot of dealers who didn't get out of the game took a beating. "They all put product in their basement and thought it was gonna turn into gold," Alan Rosen, the dealer with the self-bestowed moniker "Mr. Mint," told me. Rosen says one dealer he knows recently struggled to unload a cache of 7,000 Mike Mussina rookie cards. He asked for 25 cents apiece.