blu ray BLOWS away up scaled DVD!
I've found that CGI shows off Blu-Ray the best.
For example, I have Cars on DVD and Blu-Ray, and have watched both on the same 40" 1080p TV. The Blu-Ray version has such lush, crisp visuals... far, far superior to DVD. But then, if you are going to render your graphics at 1920x1080, what do you expect ;-)
For Film-based movies, I think the difference is less obvious. Sure, you'll get some enhanced detail, but it's nowhere near as clear-cut as you'll see with rendered wares.
Anyhoo, this is just a subjective opinion, and everyone else is entitled to think whatever they like :-)