I think you underestimate the tech getting cheaper quickly, hell one of those 3D camera phones that's been out a year or two is damn near HD if it isn't, be more optimistic!
I'm sure it was a qHD display which is only 1/4 of HD, the HTC Evo 3D.
FE:A remains the only game where it's actually looked like the stuff was coming off the screen. Birds flying by and the cinders when something is on fire in particular, I thought a little bug was buzzing around my head.
I never use the 3D in AC though, can't tell much of a difference other than having to hold the system incredibly still.
I love when things float of FE. That bird scared me first time round and the 3D snow particles? Unbeatable.