I found some useful discussion going on in the news groups.
try doing a google groups search in
alt.movies.david-lynch
There’s a Chap called trichome who really seams to know his shit, he has a lot of cool ideas. Try searching his name as well.
I do find over analysis takes a lot of the fun out of the film, but you do need to look a bit deeper in MD, there are several layers to this.