I've actually considered that. I'm too busy right now for such an undertaking but I think it would be a fun summer "project". I say project because I don't speak spanish fluently, but since my friends are not fluent in French and still read Les Mis I have hope haha.
Don Quixote is not as hard to digest as one might think, but it can be an undertaking if you're not fluent in Spanish. If you'd like something shorter I recommend any of Borges' short fiction, it's some of the best stuff you'll read in Spanish.