Contrary to most, i think it would've sold less units without the 3D.at least at the same pricepoint.
I bought mine at launch because i thought the 3D was supercool in Pilotwings. Plus it had SSFIV 3D also.Now im really used to it and i dont find it that amazing. As of late only Bravely Default has wow'ed me in that regard.

But for newcomers it sure is a cool feature to care for.