I haven't played Spirit Tracks yet, but that theme sounds great. I mean, we've all heard it plenty already thanks to the trailers...
To be honest, I really don't like the same old songs being used as a main theme. In Link to the Past, the Dark World theme was the superior overworld theme. Many of NSMB Wii's overworld themes bother me, as they're simply taken from the DS (worse, the main one isn't even as good as the DS version).
Remember SMB3, or Super Mario World? The soundtracks were unique and amazing, which helps give the games their own identity. It would've sucked if they just used remixes of the original themes. Zelda is the same. That's one of the reasons Ocarina is more memorable than the others - the soundtrack is so awesome, that it gets used in future games Zeldas (though I'd prefer that didn't actually happen).
edit: Made it clear I wasn't referring to SSB, which is all about the nostalgia / fanservice, so it's all good!
I hope Zelda Wii gets its own overworld theme!
