I'm kinda battling myself on this. On one hand, I absolutely love Casino Palace and Aeropolis. On the other hand, Port Town would've worked just as well as Aeropolis (they're both laid back). As for not using the character themes, I can't really come up with an explanation as there's two for the Wario stage.
Also, I really wish they had used "Challenge of the Bloody Chain", but since it's a Big Blue remix it probably couldn't be used due to the Big Blue stage.