Don't have time to read other comments, but I think that you make a good case for using Narnia and its fandom as an example of how personal mythologies shape literary mythologies - that is, how the stories we live shape how we interact with stories. I know I wrote fix it fic for Narnia in part to rationalise the emotional investment I had made in it as a kid, with the huge problems and resentment I had with it as an adult. Similarly, look at how the kids in Bridge to Terebithia interact with Narnia, vs Neil Gaiman's story The Problem of Susan.