Oh please don't fill me with false hopes of a day when old games are reasonably priced.
That said personally I think our savior will be pirate repro carts.
Probably comparably... in DVD cartoon collection, years ago Shout Factory's Transformers Matrix of Leadership used to be $200 used while their GI Joe footlocker (and Time Life's Real Ghostbusters) were like $80 and getting lower. It was assumed this was because the existance of a bootleg of the Matrix of Leadership set (there is no comparable bootleg of the other two things) had made the real thing more desirable... but years later, the situation reversed: You can now get a legit Matrix of Leadership set for sixty bucks (And in fact, I did) while the GI Joe Footlocker and the Time Life Real Ghostbusters both go for $300-$500 on used markets, and a part of me at least thinks this might be because of that same bootleg--people who really want a Matrix can get the hong kong one, while if you want a GI Joe footlocker or all the special features of Real Ghostbusters, you have only one option.
I wonder if Earthbound will be the same in a few years.
Right now the console I see gaining in value is the TurboGrafx, hucards specifically, because I almost never see those get bootleged. I dunno why, because its definitely possible, but it just doesn't seem to happen very often.