I actually still collect trading cards and I actually have a few of the same cards you have above. I have 1975 & 76 Topps Hank Aaron's as well as a 1976 Topps Joe Greene and a 1982 Topps Joe Montana.
@-monolith- just like you and @CamaroDMD I too have some of your baseball cards. Back in those days we didn't think to preserve our cards. In those days we used the cards to flip, scale and create motorcycle sounds in our bicycle spokes. That's why the 'two' cards I'm posting are in such 'fantastic' condition. I had a friend back then who's father worked for Topps. He gave me 'one' card. It was a large card with lots of other cards on it. It's actually an uncut sheet. There's multiple Hall of Famers on it. Unfortunately it has seen better days. The other card with Sandy, Juan, Bob and Gaylord on it I collected myself. Again, it has seen better days.
Even at a young age I knew the sports cards and comic books were valuable. I kept everything in mylar bags / card holders and stored in boxes. Everything I had was in pristine condition and yet no one was willing to pay what the stuff was worth, they wanted to pay pennies on the dollar.