Yes old films can look amazing on Blu-Ray and sometimes a lot better than modern films. I have a few and they don't look that much better than the DVD versions especially watching them on an upscaling DVD player connected with HDMI.
The best example is Blade Runner IMO.
Most movies can be put on Blu-Ray in 1080p Hi Def as they were shot and stored on film, now film was designed to be shown on giant cinema screens so already have the resolution needed to enable a HD version to be made. The have to scan them in to a computer to get the raw data and then work some magic on it. It has nothing to do with modern films being shot digitally,
Movies on 35mm film will resolve at least 4K resolution, which is 4096 pixels by 3112 pixels.... thats about 3x the resolution of HD at 1920 by 1080.
In the case of Blade Runner the action scenes and such were scanned at even higher resolution that the rest of the film to really capture the detail.
With the audio they can remix what they have to get a surround version of the sound. Not hard to do these days.
Here is a good link to an article about restoration of the Blade Runner film for HD and also all other Films in the company archives. Its crazy the amount of space the Raw 4K scanned films take.
http://www.soundandvisionmag.com/fea...ting-edge.html