I think the Necromancer/Galadriel stuff is needed in order to give the story some depth. That's what keeps it from just
being "following a little band of Dwarves around."
After all, the book has Gandalf appearing and disappearing apparently for no reason, until at the end he reveals, "Sorry I couldn't be there when you needed me, guys, but my friends and I had to get rid of the Necromancer." To which the natural reaction is, "You got rid of who?" And the story is substantially lighter.