I doubt it's anything substantial
But hey, like everything else in Galaxy it's a step up from what you normally get from Nintendo when you finish with a 100%. While I do think Galaxy is the best thing Nintendo has made since the SNES era (I don't have a hard on for their N64 games like most other people), it suffers a bit from Nintendo trying to pander to everyone.
The Manta Ray levels are horrendous, some of the open Mario 64-esc worlds are pretty boring, purple coin hunts (though I liked the timed ones), underused powerups, a little too much story, and the hub world (can we please get rid of these). Thankfully, unlike the travesty that was Sunshine, these problems take up a small percentage of the game. Hopefully in the next one they'll completely cut the bullshit and stick with the mostly linear action set pieces the way a Mario game should be.