Music alone justifies the Sonic games, this is true.
That being said, something that neither Sonic nor Mario ever did was to make a 3D rendition of the 2D gameplay. Mario went the open-ended route, Sonic went the extra-mechanics route. Both saw their fair share of humiliation (I don't think highly of Mario Sunshine). But seriously, maybe Sonic doesn't need to be innovative? Maybe, just maybe, the old formula applied to the 3D plane, nothing more and nothing less, wouldn't be a bad idea. You know, actual platforming, spin-dashing through walls, running across water, zone-specific stunts, extra character abilities that were fun/useful without being mandatory, SUPER SONIC IN STAGES, that kind of stuff.
I'm on my Wii and can't be bothered to edit your post so you can the focus I'm going for, but Super Mario Galaxy not only laughs at this statement, it's mooning you from the moon as well.

Seriously, off the top of my head, there's:
- Dino Pirahna in Good Egg
- All of Gusty Garden Galaxy
- All of Sand Dune Galaxy (with the first star having one of the best literal applications of point A to point B sidescrolling platforming in a while)
- Certain Freezeflame Galaxy stars (race, Hot & Cold Collide)
- Melty. Molten. Motherfukken. Galaxy. (Delicious gaming crack. More so for a platformer whore like me.

)
- All of the Bowser/most Bowser Jr. levels, especially the magnificent Center of The Universe.
And lots more that I have to play & remind myself of.
...
[tornado fang], why am I doing this and not playing Galaxy again?