Yes, I resized it and I was shocked with the results.
Anyway, in SMM Wii U a lot things are 3D models, but in SMM 3DS the only 3D object IIRC is Mario and Yoshi, everything else is a
compressed 2D image.
BTW, NSMBW, NSMBU, SMM Wii U and SMM 3DS share the same Mario Model. (NSMB2 doesn't)
The reason Mario looks like shit in SMM 3DS is that the model is low-poly.
Let me recap, SMM 3DS uses the same Mario Model and textures as NSMBU, but they made the model low-poly and the textures compressed and downscaled. (32×32 and compressed)
The textures in NSMBU were 128×128 uncompressed and the model had an acceptable amount of polys.