I think the main aim of a remaster should be to introduce a classic game to a new audience while making it more playable for those of us who played it before. Better controls, updated graphics and sound while keeping the essence of the original. Having the originals included is always a bonus. It's why the C&C collection was so good.
If I could see any game remastered it would be Midwinter for the Atari ST. I loved it when it came out, despite it being hard to control. A new version would be amazing.
Nightdive Studios are one of the best at remasters, they obviously love the games they work on.