I tend to agree with Matt, the main example being the revamped Turrican soundtracks. They just don't sound right. In most cases the charm of the tunes is also on the sounds used and if you change them, then it's not nice. Newer doesn't always mean better and I believe the composition alone does not make the tunes what they are, it's also the choice of instruments to make it a whole piece.
A friend of mine went back to his old Amiga MODs and revamped them the right way: found what samples he was sing, re-sampled that in much higher quality and gave them a general production facelift. Tunes sound fantastic and still keep the timbres of the originals.
PS: Hello Mark!