I think we can all agree that question is poor as-asked.
Why do these comments imply collecting is off-topic? We've got a tag for it and everything.
This is entirely opinion based, our site does not hand poll questions at all or extended discussions. This type of question would be a much better fit on a forum or reddit. – Joshua Aslan Smith
Welcome to RPG.SE. This question is not answerable in its current format. You should give a look at the FAQ about good subjective/Bad subjective. – Mouhgouda
1 The banner fibs as I didn't mark this as primarily opinion-based but too broad. This could be quantifiable if sufficiently narrowed. For example, a history of gaming question focused on severely limited-print-run professionally produced RPGs (i.e. not vanity press, not self-published) should be within the site's scope. – Hey I Can Chan
This is the kind of question that doesn't have a stable answer, though. Five, ten years from now, the most rare/obscure/expensive/hard-to-find RPG might be one that hasn't even been published today. – SevenSidedDie
@user23715 It's not a problem when it's the exception. When every possible answer to a question must eventually become stale though, that's a sign that the question doesn't suit this site. – SevenSidedDie
@SevenSidedDie meta disagrees – the dark wanderer
Consider if the question were asked on a theoretical stamps.se as "what is the rarest collectable stamp in the world?" that would be a fine question for the SE format (unless the site has weird rules). A question like this could be a good fit for our site, but the criteria are not yet well defined. OP, I recommend 'rarest collectible fantasy RPG' or 'most expensive fantasy RPG system' as potential distillations of your current criteria. – the dark wanderer
4 The one I've been designing over the last few years. There's only one copy that was ever made, and it's stored in a medium (my own memory) that only one person in history has ever had the ability to read. Is that obscure enough for you? – Matthew Najmon
1 @thedarkwanderer That meta would be relevant if this was a good question for the site now, but it isn't. I didn't say that was the reason for closing, either, I said it was a sign — a red flag. A hypothetical stamps.SE is not a legit comparison either: in numismatics, rarity is largely the point of the hobby, and knowing rarity would be the main line of expertise on an SE. That's quite different from the point of RPG.SE, and detailed tracking of every book's rarity is quite distant from our core competency. – SevenSidedDie
1 @thedarkwanderer As for your suggested edit, cross off "most expensive" (which is at least quantifiable with tools we have) — that would be a duplicate. "Rarest" is unfortunately unquantifiable with existing tools (and possibly a meaningless question anyway, as Matthew Najmon demonstrated). – SevenSidedDie
Folks, take this to meta or chat. Comments are not for discussion. – Brian Ballsun-Stanton♦