One of the very few "director's cut" editions that improved a film was Blade Runner, and that mostly by taking things out (Ford's awful voiceover, demanded by the studio and recorded basically under duress).
I am a big fan of the Aliens director's cut, since it restores the frankly crucial context that Ripley had a daughter who aged and died while she was in cryosleep. Suddenly her attachment to Newt has more meaning and the movie has a subtext that the theatrical cut lacked.
