I still buy DVDs for rarer films that I think may or may not ever come out on BD. Part of the reason is that I have a very good upconverter built into my PS3. DVDs look pretty damn good on my 60" TV when they're converted to 1080p. Not all of them do, but if they have a good encoding from a good master, it's sometimes hard to tell the difference between a DVD and a BD.
If I have an option to buy DVD or BD, I'll buy the BD. But otherwise, when I find a movie (especially a rare one like "Dreamchild" or "Girl of the Night" or "The Phantom Tollbooth") that I really want to own, I'll definitely buy it on DVD.
Also, movies from the '70s were all (with very few exceptions) filmed on very lousy film stock. This was partly due to a trend in capturing a certain "grainy" low-light look, and partly to save money for the studios. There was also an odd return in the early 1970s (actually late '60s, too) to Mono sound. It wasn't until the late '70s sci-fi movies that sound went back to stereo, let alone surround, as the norm.
With that in mind, many '70s movies on DVD are looking pretty much as good as they can, and if you buy a BD of them, they don't look any better. They're still grainy, low-light, flat, etc. Movies like "The Goodbye Girl" or "The Godfather" or "Jaws" are fine (for me) on DVD. I actually own the DVD and BD of The Godfather trilogy because the latter was a gift, and I've compared the two visually. Not much difference. Same with Close Encounters (although the audio is a big improvement on BD).
So it's up to you, ray! With newer movies, you can definitely tell the difference between DVD and BD. And there are some older 1940s-1950s classics that look incredible on BD now (Ten Commandments, Gigi, American in Paris, Red Shoes, Casablanca, It's a Wonderful Life). It all depends on how good the original source material was, and how meticulous the restoration was.
"Jaws is the Citizen Kane of movies."
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