It's hard to gauge if there are more collectors entering the hobby than leaving. Lowering prices would suggest the supply is increasing again, which I assume means more people are unloading collections than starting them, but that's for more educated people than me to suss out.
@Bronty I agree with you, to a point, that collecting is the height of materialism, but I think you're ignoring how emotions can play into collecting. Given that games contain an experiential component, though, and are not simply tchotchkes to set on a shelf, some collections can be multidimensional. That guy buying an NES Barbie cart with no intent to play it is buying a tchotchke, but someone buying a Super Mario Bros. 3 cart because they want to play it, have it to look at, and wax nostalgic whenever they see it is buying both a collectible and something linked to the human experience. The NES Barbie cart may even be looked at in a different light, where an NES cart set is the goal, and Barbie merely a piece of the puzzle. One doesn't need to appreciate every piece of a puzzle to find satisfaction and enjoyment out of the finished whole.
I would argue that true materialism is buying something simply because you can, and show it off simply because you have it. When items become status symbols rather than part of meaningful actions in life, then the acquiring thereof is materialistic.