Personally, if a character is significantly different from those from its series (Bowser, for example), they should get their own theme. I would prefer just a small jingle/fanfare, like we have now, but full songs could work for a few Characters (ones with a sort of "Result Screen" song after their victory jingle, like Cloud). This is mainly due to the fact that some characters don't have a song that is either A) the right style for a "Result Screen" song or B) Don't even have a song to begin with.