You guys gotta understand that there are still cards floating around worth $100s from those eras. I mean, today's cards, we're talking literally $10's of thousands of LeBron autographed rookies and stuff.
But if you got cards from the 1930's, each one is worth at least a couple bucks. And today's "commons" like a regular card of Pujols, Griffey, Jeter, etc. are worth exponentially more than "commons" of 80s/90s stars like Don Mattingly, Dan Marino, Jose Canseco. Those sh1ts are worthless unless you got an error card or something..it's the industry's own fault since they started mass producing the cards to no end.
The game has changed, the companies are smarter. Anyone investing now is pretty smart honestly, market has never been so cheap for "commons"...since a lot of collectors buy a case and basically donate the regular cards, just keeping the rookies/autographs.
You can buy a box of 2,000 or so cards (with stars) from the past year for about $10. If you take the time to dig through the box and sell them by team or player or something, you can make a couple bucks. Give it time, a few decades from now, the cards from today will be worth something. I'm not saying prices like cards from the 50s/60s, but they'll at least be worth a few dollars per card.