It all depends what "collectable" (or "collectible") means. I think people on this board conflate "collectable" with present or future "scarcity". While scarcity will no doubt affect its collectability, I don't think its a necessary condition. [After all, there are a lot of scarce (and very expensive) D&D items that I would never pay money for unless it was for a very informed investment decision].
I don't think I care that there are zillions of these
DCC modules in existence. I happen to like the modules, particularly the old school format and old school artwork. And for this reason they are collectable -- to me --and perhaps for many others. Now, do I expect them to appreciate? Probably not, but that's a very different concern than deciding whether or not they should be collected.