If you use comics as an example (and it is a good one), you basically support my theory. Yes, comics were somewhat reinvented. Yes, there are recent issues that are worth a lot of money. But no, no comic will ever be published now or in the future that will be worth as much as Action Comics #1, or Amazing Fantasy #15. Historically, with any type of collecting, the first items produced are worth the most, whether it is Coke bottles, electric trains or RPG's. The reasons are easy to pinpoint. Let's take D&D, and jump 40 years into the future. At that juncture, woodies would probably be worth $10,000, but 3rd edition stuff would be worth a few hundred at best. Why? 1,000 first print woodies were printed. Right now, anything that WoTC decides to send to print is going to have a six-digit print run. And if it does well, it gets another six-digit run.
So 40 years from now, if I am a collector, am I going to pay big bucks for 3rd edition stuff, or am I going to pay big bucks for a woody?
Another consideration is that old modules look and feel old. That in itself makes them appeal to collectors. Compare a newer comic book to, say, Avengers #1 and what is the difference? Modernized art, different paper, etc. The newer comic LOOKS new, and therefore is not nearly as desireable to a collector.
Nope, no holy grails in the future.