Which would be a decline when the population is growing and people ditching the print version aren't transferring to the digital. There's no way to know an accurate number at this point. It's certainly more than the measurements you used based off of those numbers and the presence on numerous other social media forums, internet sales, and how unlikely it would be for the group in your measurements to be the ones entirely responsible for the increased popularity of moderns/collectable bullion. It's simply to easy for someone to be a collector and no one to know they are which is a very real thing, especially with younger collectors. As far as serious or not I can almost guarantee we will have very different definitions of which ones should be included in that
I think one of the better barometers for our coin hobby is Ebay. It is a huge marketplace and by far the biggest place there is to buy coins. I don't know if Ebay would ever release how many coin transactions they do annually but it's gotta be a very big number
I can only speak for myself, I know I can find most of what I collect on ebay so I do a lot of buying on ebay and I sell on ebay too. duplicates and item I've lost interst in and find even on eBay prices seem to be high on some item and some guys are asking prices are 3 to 4 times what the prices should be and everything they list as "rare" even common date items are "rare". I do go to some of the local coin shows and most of the dealers have just bullion or common stuff and asking top dollar. I will say that I am a member of the ANA and NGC. I have 10 32qt plastic boxes of coins so I am a collector.
Someone early in this thread mentioned the 09-SVDB and 14-D cents and commented as to how they are not "rare" but are overpriced. I have wanted an Alexander the Great Tetradrachm and an Athena Owl for quite some time, and they are not "rare" yet the prices on them are HIGH because of popularity. I know these are ancients, but the rare/popular paradigm is still there.
Dealers who refuse to lower prices and take a loss will lose in the long term to those who are more realistic. Collector dollars will continue flowing to dealers who sell what collectors consider to be reasonably priced coins. I have been adding to a Seated Liberty Half Dollar collection for several years and notice rising prices for key and semi-key dates even though the demand does not appear to be strong. Searching eBay for some dates brings up no offerings -- for months on end. So why is it that offerings for key date Lincoln Cents are numerous and yet the asking or starting price does not reflect this? I think that along with dealers not wanting to take a loss we must also consider delusion and ego.
Those half dollar issues are actually rare so they just don't show up. That's why you may not see one for months. Demand may not appear to be strong but that is because the number of people that collect seated halves by date and mint is pretty small. But prices are high because the number of coins available is still less than the small number of collectors Here you have the fct that the coins are fairly common so they show up all the time, but there are a LOT more Lincoln cent collectors that there are Seated half collectors and there are once again more collectors than there are for these merely scarce coins so the price gets bid up. And with a Lincoln cent up for bid there may be hundreds of people interested in it whereas in the case of a scarce seated half there may only be a dozen or two. So activity on the cent is higher.