Cool! I read Campbell as well as Manly P. Hall, and I've touched on Jung as well. I totally get the metaphorical aspect. The Power of Myth marked the very moment when I realized I don't believe in a personal god.
A little bit of philosophy makes one an atheist. A bit more, aaand ya know.
I totally get the metaphor of the monomyth (birth, youth, adulthood, death...), and I wrote in a reply just last night quite directly about this.
There's absolutely a place for rationalism. I do consider myself a rationalist, naturalist, and not a spiritualist. However, as Campbell alluded, we lose some of the experience with that too. It's a two-edged sword.