I've been thinking about this for a while because there are always threads about the hobby in decline popping up regularly. I'm also starting to come around to the theory that the hobby is very healthy as it currently is and don't worry about the kids.
Everybody is worried since kids don't collect cards like they did when they were young. However, do we hear about card companies going out of business because they lose too much money printing cards? Nope (they only go out when they don't get licenses from MLB). So then the card companies must still be selling enough to do just fine even if they're selling to more adults these days then kids. Face it, as others have mentioned, kids have a lot of other entertainment options these days. That's just how it is.
Secondly, I read things such as
Link postings from Heritage telling about record revenue in Sports Memorabilia and other collectibles like coins. Let's talk coins. According to that article Heritage had nearly 200 million in revenue last year in colin auctions (compared to 16+ million in Sports Collectibles). Those are huge numbers. Now how many kids these days do you know that collect coins? Heck, probably fewer than collect baseball cards! (Granted it is a lot cheaper to start a coin collection, like if you wanted to start w/ the 50 states quarter collection.) I'm not a coin collector, but I don't think those collectors are too worried about their hobby dying out.
Lastly, why do people really care about the hobby on the decline? Sure, it's boring if there are fewer and fewer people in the hobby to chat with and the fact that you are constantly losing an enormous wealth of knowledge in the hobby. However, if you are concerned about pricing dropping, that just means that there are more cards that you can afford to buy and put into your own collection. If you are worried about your own value of your collection going down because of resale value in the future, then go back to the article from Heritage and others which show that sales in the hobby are going up. No doubt that there are particular areas that are going down in value, but that's more reflective of collecting tastes changing which may be cyclical. You still have to be smart about buying cards (like not overpaying) for financial reasons, but the decline of the hobby will not be the reason why your collection has gone down in value.