Well to me it depends on how it's done. Mania's essentially in a different league from Sonic 4 and Sonic 3 in what, where, and how these games reuse existing material. Sonic 4 (primarily Epi. I) was a case of every zone, enemy, and boss channeling something that was not only old, but something widely recognized. And in most cases, they weren't relatively different takes on the old material either; a lot of the reused badniks, level identities, and bosses were straight regurgitations of the original source material. In some cases, the reused material was actually dumbed down from its original incarnation (Bubbles being neutered of its spikes --unless they were colored red-- and free movement, existing only as static homing attack chains). Epi. II had more fresh direction at this, but not by much. Sonic & Knuckles' Sky Sanctuary boss revisits are essentially similar to the originals in how they play out, and the revisits themselves are fairly easy to point out. But the context they are used (by Mecha Sonic, and serve to slow down Sonic and co. instead of acting as actual boss fights) is different, and they are essentially the only time the game engages in throwbacks in this fashion. The rest of Sky Sanctuary could otherwise be described as relatively original. Mania's Studiopolis, for all of its references it has, are largely comprised of obscure stuff that I don't think the general public / casual gamers, or even casual Sonic fans would widely recognize. The Popcorn Shop or the aforementioned star bumpers that may be from Knuckles Chaotix I doubt most people could single out right off the bat. And a handful of it isn't even Sonic in particular, with stuff like the Daytona USA van, Game Gear TV insignia, and the Streets of Rage sign. Even then, the overall level identity/level theme is anything but familiar. Overall I'm fine with the way Studiopolis has gone with it; though I do understand and generally agree with your main point on how you want the game's other original levels to be light on the throwbacks and shout-outs.