This reminds me in a similar way to the stamp market. A few decades ago, stamp collecting was as popular as ever. Nowadays, except for a very small amount of rarities such as the Inverted Jenny, prices for most are a fraction of what they once were. This also applies to postcards and baseball cards for the same "nostalgic" reasons since the younger generation doesn't quite have the fond memories (though it seems like Comic Books are popular among Gen X and Millenials after a bit of a lull in the '90s).
That said, most coin collections are compact in storage and don't take up a lot of space. In terms of history, you could even associate more recent decades with their usage in many ways. For example, in the 1950s a single
Franklin half dollar could have purchased a showing at the local movie theater to see the latest film in 3D or Cinemascope, a burger and fries (or shake) at a local diner such as the one on Happy Days, a blackberry pie, pecan clusters, five cans of Campbell's Tomato Soup, a couple gallons of gas, or ten records of early Rock 'n Roll music on the jukebox. The 1930s with dimes popularized by a famous song involving the depression, or even the 1900s
Indian Head cent where you could purchase the daily paper, a piece of candy, or see a "moving picture" at the Nickelodeon with a
V nickel (another series that has gone down in price despite being older).
That said, I find this to be a great buying opportunity for some of the popular late 19th/early 20th century coins since along as America exists, these coins will always represent a place in history and I'm sure there will be many completists (like myself that I aspire to be) who seek each coin, with quality coming next. I've recently been buying more coins over the past couple of years compared to the late 2000s/early 2010s when metals/popular prices were at their peak, especially as I've progressed with a higher income giving me more dispensable cash.
Also, there is the fact that most coins nowadays don't purchase much unless if you have a deep pocket full of them. With credit cards, electronic payment system, and cash used for necessary services that require a minimum of at least five bucks, most view coins as a product that has long outlived their usefulness. I haven't used a payphone in over a decade nor have I used a newsstand to purchase a paper and I could probably count the number of times on my hand that I've used the vending machine or parking meter to deposit coins. I just dump them in my bank's coin counter when I visit.
However, coins still have that intrinsic value that paper/plastic/bytes never could accomplish which is why I'll still collect them. Its so much better than owning stocks which are all-electronic nowadays and are even more volatile than coins.
The earliest example of this downtrend in these "popular" products were the modern (post-1964) proof sets. I recently purchased several from the '80s/'90s at a coin show for just three bucks each, and a good example of this is the 1999 Proof Set. Back in the early 2000s, it would frequently sell for $100 or more, and nowadays, the barely sell for around $10 on
ebay when sold, and the entire 2000s (plus 1999) for around $100. The 1995 Prestige Proof Set nowadays can often be had for less (around $50) than what the regular clad set sold for in the late '90s/early '00s (around $75, which sadly today is worth around a tenth of that value, and less if your factor inflation). I purchased a 1995-S for around $35 bucks around 2003 because I thought it was a great deal, only to discover that it was in the stages of a steep decline in value. That said, I feel that once the value of a coin or set gets so low, I feel that the risk factor diminishes since there is less of an opportunity for a decline in prices. Late 1960s-2000s Proof Sets are in the ultimate buyer's market; they may not go up much in value immediately, but these still represent the finest quality of coins minted and of course can be used to represent a time in history (Hippies/protest marches, disco, Reaganomics, the Internet boom, and the War against Terror and Iraq). As always, time will only tell with the value of coins in the future and just like stocks, its all speculation and never a conclusion.