Well, it worked for C.S. Lewis, who also has broader appeal. His fantasy novels work better as Christian apologetics than his Christian apologetic essays do. In my opinion, for what it's worth*. And Tolkien was probably more influenced by Norse mythology.

Some of the most enduring works of fiction, though, weren't written with demographics in mind, but with just one or two people as the original intended audience - like the Alice books. I have major issues with the concept of demographics, anyway, as they tend to be divisive. A book with a young protagonist isn't necessarily "for" young people. Books with female leads aren't "for" women. Books featuring people of color aren't just "for" Western minorities. We can all learn something from different points of view, and we don't all fit neatly into pigeonholes. Some of us don't even like pigeons.


*For those who may not be aware, the word "apologetic" in this context has nothing to do with being sorry for something, but a reasoned defense of a religion.