"Improvements" are often in the ear of the beholder. This goes both ways--what you or I might consider a bad idea might have sounded great to somebody else in the audience.

Reserve judgment on changing to 4/4 time and simplifying chord structures since I think it depends on the song. I've heard songs that were injured by this but I've also heard songs that had more chords than they needed and did better with less pretentious chord progressions.

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A local neo-Celtic band recorded a version of "Wild Geese", which uses the tune to "Planxty John Irwin", and changed it from 3/4 time to a reggae beat. Some people were put off by it, but overall it worked out very well. I say that, and I don't even like reggae.

Come to think of it, right now I'm listening to "Deux-Pas des Condamnés", which is a two-step that is normally "Valse des Condamnés" in--you guessed it--waltz time. Works great either way.

For both songs, it would have been a pity if they hadn't at least tried the new version, even if it was "wrong".