Yes it will!
-Pokemon innovation. Using AR cards to play? I see this as a huge thing.
-3D without glasses? Very attractive..
-New Mario......
-More children aging to an age where they can play video games.
-3rd party support.
-Video chat, movies, mp3...etc!
-3DS looks more attractive and not bulky when the DS released.
People fail to realize that as years pass people upgrade and new people are born! This is why the DS was able to sell so much even when the Gameboy and Gameboy Advance made mind blowing numbers, yet it didn't stop the success of the DS.
I doubt the gap between NGP and 3DS will be smaller. I expect almost the same ratio especially when the NGP will cost more than the already pricey 3DS. Not many people would buy that once they compare it to the 3DS.