Exactly. I'm pretty sure one can find "lots of timeless wisdom" in the Koran, the Bhagavad Gita, the Epic of Gilgamesh, the Norse Prose Edda and Poetic Edda, the Necronomicon, etc., etc.
Yes. But the Necronomicon is one of two things (depending on what you're talking about): A fictional grimoire, or a piece of fiction (a hoax, even).
I know, throwing that in was my lame attempt at humor. :-)
especially in the age of limited literacy and scribal skills, I'm not sure people would have invested much time in copying and archiving ideas and texts they thought were garbage. this is sort of a literary survivorship bias at play, it would seem.