Downward trend in card values?

[steve B]

Pretty much all collectibles go through cycles, particular things are popular for a time, then people move on to other stuff. Some of that is interest, some of it publicity, some of it just changing opinions on what is worth something.

When I started, cards were just beginning to be "valuable" nearly every postwar card was relatively inexpensive. The 52 Mantle hadn't topped 1000, and a decent Aaron rookie was 60. Hardly anyone collected the few insert sets and obscure stuff was either dirt cheap or really expensive (for then)

I've been into collecting a lot of stuff over the years, some hobbies have grown, some have not.

Coins
Stamps
Old Bottles
Beer cans
Telephone/telegraph insulators
Old radios
Old computers
Old bicycles
Action figures
Old books
Old magazines

All of them have seen some of the same things since the mid-late 90's. I've seen it called the Ebay effect.
Before Ebay, a lot of that stuff had value even for the relatively common things. (Old computers being the exception, they weren't old enough for the usual yard sale crowd. ) So you might see one reasonably nice old radio or bike a year if you went to yard sales and flea markets. More often if you were really into it and went constantly. So you bought what you could find at what seemed like a reasonable price.
Once Ebay got big enough you could find nice stuff a lot more often. Like anytime you felt like looking. And pretty soon people caught on to just how common the common stuff really is. That's true for any hobby. And once you realize that you can buy a perfect or near perfect example pretty much whenever you want to, there's no need to buy the lesser ones.
Late 90's I did pretty well buying boxes of late 80's cards for almost nothing, and selling lots of 100-400 for a few dollars. (Not counting the time I spent, which is only one reason I stopped) By say 2005 those lots wouldn't sell as well. Maybe half the time or less instead of nearly every time. People interested in random lots realized they could just buy complete sets, or much larger lots for less per card. Now there's a lot of "cheap" singles listed, commons I'd maybe want a few cents for listed for $1. Because when you need one card, it's easier to just buy it even of it's massively overpriced because in the end, it's just a dollar.

The really good stuff either continues to be really good with ups and downs, or it essentially goes into hiding until the prices come back up. (Old computers were very pricy for a while because all the dotcom guys were buying up the stuff they learned on or had as kids. )

Most hobbies never really die, they just change.

Steve B