I can't think of anything clever for the lighting, because Colors Ultimate is basically the opposite problem; everything is darker and moodier rather than lighter and sterile, and lighting effects are blown out with bloom rather than being removed altogether. I can't really think of a fair comparison in terms of the overall quality of the game either. It would have to be an okay-ish attraction and some completely dysfunctional, demonstrably worse version that replaced it.
Meetable characters in a Sonic-themed land is something I hadn't even considered until now. Aside from the obvious ones like Sonic, Tails, Knuckles, Amy, Shadow, and Eggman, I think pretty much all the "Worldian" characters deserve costumed representation, even if some of them would only appear on rare occasions. Blaze, Rouge, Silver, the Chaotix, the Babylon Rogues, and even obscure characters like Marine, Honey, and the Hooligans would all be great.
The un-stylized human characters would be odd, though. I wouldn't really want to see Merlina or Shahra and whatnot outside of maybe some sort of special event. Robots such as Omega and G-merl are possible, although I have no idea how you would make effective costumes for them.