There are some advantages to being older

It means that I have some hard-to-find but sought-after games simply because I was around when they first came out!

Probably the best example of that is the Holy Grail of wargames, Up Front! This card came has a well-deserved reputation for being an excellent game (although with tough rules) and it can be hard to come by in good condition without paying a lot. And it's becoming pretty likely that it will never again reappear, at least not in its current form. Even tougher to find are its expansions.

Another classic and beloved old Avalon Hill game that will never be reprinted in the same form is Dune. I also have the expansions for that game. This is one of the best multiplayer games out there, as well as one of the best realizations of a novel in game form.

In the case of Up Front!, the original artwork has been lost. So even though Multi-man Publishing has the rights (at last report) for a reprint, a new edition will require the same work as a new game. That project appears to have stalled however, so it seems likely that all the copies of Up Front that will ever be have are already out there.

For Dune there are plans for a reprint by Fantasy Flight Games, but it will have to be rethemed because FFG got the rights to the game system, but not the Dune license. Reportedly the theme will be set in FFG's Twilight Imperium universe. This may work just fine, but it will by definition NOT be Dune.

Ambush! is another system that I got in on the ground floor when it first came out. While copies of Ambush! are still available on eBay for reasonable prices, the expansions can be hard to find cheaply. This is a problem because, as a solitaire game, you need fresh missions for replayability.

I wasn't thinking about the long-term availability of those game system back in the day, but I do consider that now when making purchases. For example, I made certain to pick up an extra copy of Simmons Games' Bonaparte at Marengo because I suspected it would become a hard-to-find game. Simmons has since confirmed that there will be no reprint for that game.

The kind of game that's most likely to become rare are unusual designs from small publishers or those dependent on a license, as well as expansions. If you really like a game it seems worthwhile to make the effort to keep up with a series in near real time, because there is no guarantee you'll be able to get it later.

Can Dune be rethemed and still be Dune?

There's some excitement in Geekdom over word that Fantasy Flight Games is going to publish a new edition of Dune, widely considered one of the true classic of gaming. FFG is known for its excellent quality product, so rejoicing was widespread.
Ah, but wait! It turns out that FFG didn't get the licensing right from the Herbert estate, so their Dune will have to be rethemed, reportedly into FFG's Twilight Imperium universe. If so, will this still be Dune?
I don't see how it can be anything other than a brand new game that resembles Dune in its playing style.
Rethemed Euros are fairly common, because theme is definitely secondary to the game design for them. But even there, a rethemed edition will generally be considered a new game.
But with wargames theme is central, Indeed, the design achievemnt in Dune is how well the game captures the thematic elements of the Dune novel, which is no mean achievement considering the complexity of that book. From the Bene Gessert prediction, to the Atreides foresight to the spice blows the game's key elements make sense only in the Dune context. Will a Twilight Imperium edition merely copy those mecahnics and paste on some new justification? Or will the game strive to capture the spirit of the T.I. universe and come up with entirely different rules that reflect that setting? The first choice seem likely to leave fans of both dissatisfied, while the second choice will remove the game even more from being a new "Dune."
Many classic games have second and even third lives with different publishers. Games such as Diplomacy, Acquire, A House Divided, Napoleon, War at Sea and Russian Campaign have been reprinted successfully.
But some games can never be replicated, especially wargames that rely on licensing because they are set in a proprietery setting. Dune is one of those. The Avalon Hill edition will never be seen again. If you want one, ebay is your option.