I think what makes at least some difference with Scooby Doo is that it's scary/bad magic being maliciously used by unscrupulous adults to hoodwink people. So the message isn't "The world is drearier and less wonderful than you realized" but rather "The world is safer and less scary than you thought." I think a Newbery-esque book in which the child protagonist was terrorized by someone using fake ghosts and then rescued by their friends wouldn't have the same disillusioning feeling at all.