One thing I've noticed, having bought both the DVD and Blu-ray versions of these movies, is there's not a whole lot of difference between the Blu-ray and the DVD when it's played on a Blu-ray player. When I play the DVD on the standard DVD player, the difference is like night and day. The colors are much more vibrant, the detail is profoundly sharper. I put the DVD on pause and did the same for the Blu-ray, then switched inputs to compare several times. I was unable to do the same with the when comparing the DVD on a Blu-ray player; I only have one of those players. Still, I paused at the same point and then removed the disk and replaced it with the Bu-ray disk. I did not percieve much, if any difference. It may be that my eyes are not sharp enough to pick up finer detail. It's also possible if I stared at them long enough side by side that I'd eventually notice an improved image on the Blu-ray. Be that as it may, the experiment has put to rest any concerns that I have over idea that my DVD collection has become obsolete and outdated.
In case anyone is wondering, I bought both versions because I was planning to get a Blu-ray player when I placed the order. I wanted DVD copies because I know I'm going to want to bring them to other people's houses to watch. I sometimes use HODS when I teach Dracula. Having the students compare and find counterparts for characters in the novel is an activity they enjoy.