[Cthulhu_]

Which is of course highly subjective; you could argue that film grain is an unwanted but unavoidable side-effect from the medium used, just like other artifacts from film - vertical alignment issues, colour shifting from "film breath", 24 frames per second, or the weird sped-up look from really old films.

I don't believe these were part of the filmmaker's vision at the time, but unavoidable. Nowadays they are added again to films (and video games) on purpose to create a certain (nostalgic) effect.

[pessimizer]

I don't think this comment demonstrates an understanding of the argument. An unavoidable side-effect of the medium is part of the medium. You will consider unavoidable side-effects when you are building something for a particular medium, unless you are stupid. If that unavoidable side-effect were not part of the medium, you would have made different choices.

Colorizing a black-and-white film, for example, is not ever restoring the original intention or vision, even "subjectively." If the makers of a black-and-white film had been making a color film, they would have made different choices.

This does not mean that you should not colorize black-and-white films, you should do whatever makes you happy. I honestly can't wait until AI is recreating missing scenes or soundtracks from partially lost films, or even "re"creating entire lost films from scripts or contemporary reviews and cast lists, and expanding films to widescreen by inventing contents on the edges. But this will not be restoring a vision, this will be original work.