I always find Wonderful Christmas Time by Paul McCartney is one of the worst victims of this, looked so clean on the 1979 TOTPs, but the version show on the music channels for as long as I can remember, and even on Paul's own DVD, looks awful, looks like it's gone down several generations of both film and video, and probably a standards conversion or two as well. I have a copy of an ITV Chart Show episode from 1993 where they show it on the video vault, and they're using the awful quality version there too, only 14 years after the song came out.
It's almost like they're reading our posts, as the Paul McCartney YouTube channel uploaded an official version of the music video the other day (for some reason his music videos have never been posted officially to the site like other artists have).
It's still not great quality, certainly not a newly transferred remaster, but it does seem to have been cleaned up of scratches and dirt. I think the copy shown on TOTP 1979 is probably still the best, because you can actually see detail in dark areas rather than it just being black (and as it's a very dark video, in terms of lighting that is, that helps a lot).
But even better is this - a UHD, newly transferred version of the Last Christmas video. Wow! It almost looks wrong seeing it in such high detail like this. Worth noting by the way that the video was always shown in a 16:9 aspect ratio, originally with letterboxing of course, so it hasn't been cropped.