Super cool Boo faceplates <3
As for reasons to upgrade to N3DS, I was still rocking my launch OG system and I appreciate the faster OS, faceplates, c-stick for SSB, better 3D, and now SNES games I can see why those things don't matter to most people, though, N3DS is just a model refresh and not really a must buy if you're okay with your 3DS.
Minimal differences in resolution size for some games and better textures in MH4U (and probably other games too, though I didn't compare any others).
I feel there are more than enough reasons to get the n3DS (especially if you don't have the 3DS already).