I've a question: does the BoVD actually contain much of a discussion of the motivations of fiends and how to use them in campaigns? Does it tell you of the PCs and the material plane can get caught up in their wiles and intrigues? I'm looking for stuff on how the forces of evil fight their eternal battle with the forces of good - that sort of stuff would really be useful to me.
But, so far, I've got the impression that the BoVD is actually quite immature stuff.
As for the BoVD/BoED I think that they could be a really useful addition to D&D (of course, whether they are is another question). Loads of fantasy is based around cosmological battles between good and evil - I'm not even going to bother listing examples - some books that explore this would be great.
As for discussions of morality. I hope they do a very "Catholic" take on things. I won't pretend to know much about moral philosophy - but I think a modern take on things (e.g. utilitarianism) would just be out of place, and a battle of good vs. evil doesn't really work from, say, a buddhist perspective.
nikolai.