Late to the party, but I don't care for either of the two suggested changes (Marcy/Marle). Marcy isn't that bad (fantastic in battle, so that's what counts), and adding Marle would be like putting a giant Trigger wart on Cross' greatness. Perhaps I exaggerate, but still.
Anyway, the change I'd really like to see is some form of increased difficulty in the game. Since adding sequence breaking of some sort wouldn't be likely to happen, this is the next best thing in my eyes. Making each boss harder to the point of being ARGH would be pretty freaking awesome.
Also, the pants suggestion I can agree with (for the guys). Korcha is a moron anyway, but I'd prefer not to see a moron in bright red underwear. >_<