I know very little about Buffy (I watched the movie years ago and have only heard stuff in passing about the series), but I have watched (and read) several versions of the Nutcracker. Yours makes as much sense as any of them and more than most.

Just who is Herr Drosselmeyer? Why can he do so many things that no one else can? Why does he look down on the adults as if they were mere children? Why does he single out Clara for the gift/dream? What is the dream's purpose? Is it real?

You've explained everything. Thanks for sharing.