On the gimmick versus non-gimmick side-talk:
I can imagine that if the stylus is spatially aware and can relate the viewers illusion of depth to the point in 3D space they think they're seeing it would have an important immersive quality that goes beyond gimmick.
Imagine palying a puzzle game where you're dragging blocks in 3D and as you point the stylus in thin air at where you perceive the block to be it moves realistically.
If a simple thing like turning the Wiimote to open locks in Metroid Prime can add such a an element of being present in the world, melding such control with 3D would be quite groundbreaking IMO.
So 3D can be a cheap graphical trick or it can be a big step forward depending on how all the elements of control and gameplay are integrated to suspend disbelief.
If this 3DS is true 3D technology, and I'm skeptical for now, I think Nintendo will go further than mere graphics.
They have been experimenting with these concepts from before the technology was ready (Light Gun, Power Glove, Virtual Boy) so I think they are actually quite committed to VR as an ultimate goal.