Have you seen Michael Ward's Planet Narnia? I haven't had a chance to read it yet, but I will when my library copy gets in.
Ward hypothesizes that each of the books in the Chronicles of Narnia is structured around a planet, and uses the pre-Copernican, astrological symbolism in the imagery of each book.
1. The Lion, the Witch, and the Wardrobe: Jupiter
2. Prince Caspian Mars
3. The Voyage of the Dawn Treader Sun
4. The Silver Chair Moon
5. The Horse and His Boy Mercury
6. The Magician's Nephew Venus
7. The Last Battle Saturn
I was a bit skeptical when I first read this, but then I went through the books, and by Jove it seems to fit. I don't know if this is one of Lewis' central worldbuilding ideas, but I'd say the imagery is definitely there in the books.