I've heard some people voice that concern when it comes to clean-ups of older films. Most modern films - I guess since about 2008 anyway have been kinda filmed with HD in mind so they will always look super sharp and pristine. Especially the effects based films. CGI and HD go beautifully! But so does good landscape work as well. Any good DP will make whatever kinda film they use look the best it can.
The oldest film I've watched on a specific Blu-Ray release was the region 2 Psycho special edition I bought and I thought that it looked great fter 50 years - still a bit grainy in places but it came with a stonking new 5.1 sound mix that added so much to the experience of watching the film.
Dialogue was clearer (including a line spoken by Norman at the very end that was made so the original audience couldn't hear it at the time because they were concerned about the percieved sexual connotations of Norman's transvestitism), and everything sounded just so much better!
But not all transfers of older films are well done - some of newer films aren't all that well done either!
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist