It's really hard to tell the future of the game. As a previous poster stated, the game is definitely getting more popular. I'd attribute that fact to the Burger King sponsorships, this generation of video games being better than the last, and the new movie coming out. I also think that, as the recession continues on and the economy gets worse, people are not only going to be looking to card games as a (fairly) cheap form of entertainment that a whole family can enjoy together, but also, Pokemon in specific has been around so long I think the worried consumer can have more faith in it than a game that just popped up on the market.
As far as older cards being worth something...I don't think the original sets will be worth anymore than they are now. The thing with collectible games, and card games specifically, and even more specifically Pokemon, is that there are a few different types of people: One group is the hardcore player who only cares about the best cards and doesn't want any retired cards because they're not tournament legal. Then there's another group of collectors who might also play, but they mainly want to collect everything in every set. The last group (obviously there are more groups, this is just a generalization) is the group of kids, or otherwise dis-interested people who have some cards but don't play the game often, want to collect but aren't really into it, and mainly just have what they have. The problem is that Group A doesn't really care about older cards, Group B might, but chances are they have most of what they need, or they know the cheapest places to get it, and Group C might want the cards but they're not willing to shell out anything for them. I could be wrong, but if anything I see the older sets decreasing in value.
Back to the general future of the game: The bottom line is that Pokemon will stop being produced when it stops making money. I don't have figures or inside info or anything, but I'd assume that with the rapid succession of sets and the more experimental products (Premium Boxes, etc.) that the card game is doing just fine. I'd also bet that with the video game spin-offs coming out so often, that sector is doing well as well. I can't speak on the anime, but with the movies coming out still, I'd assume that's doing fine as well. The bottom line, to me, is that it's doing fine right now and I believe it'd do fine for the foreseeable future, but I'm no analyst.
tl;dr: I think the game is getting more popular and will be around for a long time, but I wouldn't invest heavily into older sets if you intend to make a profit.
