I'm not sure I agree with this. The prices that things sold at might have been cheaper 20 years ago, but the advent of the web with used-goods marketplaces has allowed people to access things that were previously not available or hard to find.
I can go onto ebay and order things from the US that were never available locally in my home country. The same with Yahoo! Auctions for items sold only to the Japanese market. And not only can I access things that I couldn't before, but I can easily search for things. Want a copy of an obscure record? No need to search dozens of local stores - Discogs will probably have a few copies for sale. Need a book to complete a collection? Try a quick search on Amazon or Abebooks.
While the prices that things sell for may be higher, I find that it is considerably easier to collect things now than it would have been before the web.
I mostly agree, but there are exceptions. For my birthday a couple years ago my son showed up with a couple cardboard boxes full of books. Turned out to be a complete set of "Great Books of the Western World," worth well over $1,000. He had picked it up for about $30 at an estate sale a couple days before.
I bought a bunch of architecture books a few years ago at an estate sale for $5. Flipped through them and my son looked them up on eBay - we sold the collection for several thousand dollars.
Nowadays half of the market is flippers and scalpers, prices have shot up, and nobody is getting a pallet of good books for a dollar anymore.