I forgot the NiD soundtrack was in the library, but it's funny that they went with the "Everything and the kitchen sink" mentality.
For the characters, the game uses BRMDL files like many other Wii games. If you can mod games like Brawl and Mario Kart Wii, in theory it should be possible to change the models in this game. One issue I encountered is that I can't find the ACTUAL location of the character models.
The "Character\Player" directory seems like it SHOULD have the character models, and it does, but changing them doesn't seem to have any effect on the game. I deleted NiGHTS' whole folder to see if this were the case, and the jester was still there.
The Reala screenshot above is the cutscene model in a completely different folder.
For the stages, I have no idea what format those are in.