i completely agree. That's why I'm kinda picky when it comes to buying older horror films. Do I really want to get a crystal clear blu ray of Romero's original NotLD?
That's entirely up to you but I do, I think. Watching older horror films and low-budget horror films in high definition or in better PQ than a VHS or a crappy rip opens up a new level of appreciation in those films. When you can see ultraclearly where the artifice lies, it adds a certain charm to the horror imo and more than anything it in involves you in the creative process. This is also why I really like watching the really crappy stuff, horror movies by Edgar Ulmer, Jess Franco, Luigi Cozzi and other slightly more sophisticated gore auteurs such as Lucio Fulci and Lamberto Bava*. The horror and gore elements are totally and utterly fake but they interest me because they teach me stuff about the building blocks of horror, gore and why it is that these films have such an effect on me. Horror films don't ever really scare me anyway (although some do), so I personally don't have to worry about "not being scared" because of high definition imagery. What it does offer me, is to see how well some of these often looked down upon movies are actually shot (bluray quality really accents all colours, cuts and camera moves) and exactly how much love and care is poured into them.
*for the record, I prefer Dario Argento and Mario Bava, but you see why mentioned the former and not the latter