I definitely pick and choose my blu-ray movie purchases carefully.
Halloween II was
released by Universal on blu-ray some years ago. The big selling point was the for the first time the "documentary"
Terror in the Aisles was a supplement on the disc--first time it was released on a digital format (and was thought to never make the jump because of the many rights issues involved in with all the movie clips.) So I definitely picked that up.
Just two years ago, Shout Factory
releases a "special edition" blu-ray with a handful new supplements and even better transfer.
I didn't bother with the newer release. Just wasn't worth a repurchase for a slightly cleaner picture and a couple new goodies.
Same thing with Disney's
Beauty and the Beast. They released a "Diamond Edition" back in 2010 on blu-ray, which I got. But last year they released a "25th Anniversary Edition" which included an extended trailer for the new live-action film. Didn't even bother to check whatever else might be new in that edition as I definitely wasn't going to buy it again.
(plus the definitive version of the movie is the CAV LD release with the original colors)So yeah, movies can be re-released over and over again, but you are by no means forced to buy them.
I sure as hell don't.
But also with blu-ray we are getting movies that weren't released on anything else save VHS. That is a good reason to upgrade, unless you like your movies in dark, grainy 240i resolution.