The best purpose for sci-fi and fantasy novels are to aid in the expansion of the reader's consciousness and idea space. This is why Dune
and God Emperor of Dune
are infinitely more interesting than the books by Brian and Kevin. Those books aren't about the universe, they're just action novels which use the Dune universe. Which is fine and valid, but there are really much better page-turner thriller books to be read. I can't see Paul of Dune
changing anybody's life.