"Melancholy Elephants" is a brilliant idea (how ironic, an original idea about the lack of original ideas), but as fiction it's a terrible story, consisting largely of a lecture delivered to a person who helplessly sputters "but ... but ..." and who is supposed to be articulate and intelligent but never shows it. Yep, this is a Heinlein homage, all right.

But yes, it's an important story. It seems to me that the really important point in it is not that ideas are finite in number, so much as the observation that the source of new art is ideas derived from previous art, works that were in the public domain but are now ceasing to go there.