Depends on the type of model:

• For characters, some of them got completely brand new models like Miss Petunia, Melody Pianissima, or the Grabbing Ghost. However, I'm pretty sure most of them use the original game models as a base, just edited for higher detail. For example, everyone has more detailed hands compared to their GameCube counterparts, and the textures are higher quality.
Then is the case of Boolossus, he isn't a recurring character, but since he is a Boo, he got the redesign treatment.
In general, I'd say the characters are better on 3DS, but it's weird to see this game with modern designs.

• Objets and Items are a bit more complicated. Some look better on 3DS, while others look superior on GameCube. A great example of this is the Game Boy Horror, which have more detail in the GameCube version.

• For the maps / rooms I haven't ripped any of those yet, but from what I read a while ago, there are definitely some noticeable differences.

• Finally there is the new things added in the 3DS version, which have completely new models and in the case of Polterpup and the Gold Bone, I'm sure they just reuse the models from Dark Moon.

So how do these models compare with the ones in the GCN game? Aside from the ones of major recurring characters who use more recent designs, I mean.