My recent reading of CASTLEVIEW forced me to appreciate for the first time just how many points of correspondence there are between it and TWK. It's hard to imagine that the former didn't have some influence on the writing of the latter, and I wonder if one book can be used to inform the understanding of the other. Of course, I don't have the answer, but maybe it would help to point out some similarities.
In both books we have a young Arthurian figure whose name isn't revealed until the end and who hails from modern America. There is a certain disconnect from an older, absent brother. We have Odin and Sleipnir, the Wild Hunt and mention of the Green Man. We have fairies and a fairy world that can be blundered into, and a young, regal, immortal fairy woman of uncertain loyalties. We have a talking cat. A big dog. Blood sucking females. An ambulance on a highway. Ghosts. Giants. A castle in the sky. The mingling of Norse and Arthurian material.
The older book takes place mostly on the American side of the indistinct boundary with Faerie, the newer on the other side. For whatever that's all worth.
-Roy