I hate this idea of upgrading but it's necesarry I guess.

So when blurays were just available did you keep your old dvd's or traded them in?

I never get rid of movies.
I only repurchase if it is worth it, either by being too cheap to pass up, or to great to not own on BR.

I don't purchase most comedies on BR, because picture clarity is not an issue for films like that.

I keep every movie I like, but I'm not opposed to selling an older-format copy for a new-format copy, like I did with Ran - I went from DVD to Blu-ray, and sold the DVD.