I'm a total sucker for Blu-Ray. I have about 50 BD discs, and I'd say about 20% of my purchases are things I already own on DVD. Thing is, I was an early adopter of DVD, and lots of the DVD discs i have are not 16x9, so I tend to update those that come out with new HD 4K transfers. Generally, I find that even older movies tend to be much cleaner-looking, and sound is definitely better.
If you're one of those that says "I only have 2 movies anyway", chances are that you aren't exactly the market they're looking for.