"What I reject, is the notion that any cartridge that is no longer made, made with this or that exotic material in the cantilever, or has some unusual property or structure (magnet, coil, stylus shape) is therefore to be sought and probably sounds better than anything one can more easily acquire or which is more conventionally constructed."
I'd reject that too — but is that really the premise? Who has the "the notion that any cartridge that is no longer made, or has some..." etc "... probably sounds better..."?
We just don't know. The only way to know is to hear it — it's a mystery and a gamble — but if an obscure and interesting cartridge shows up and ante is right, I'll take the chance. Some favorite cartridges, and other components, came to me that way.
Forgive my edits and italics; I don't think they don't alter your meaning.