Alright,
I return from Best Buy with tales of
anguish and
fortune!
It was tough goings, because even though I connected to Nintendo Zone, the coupon was nowhere to be found. Had to talk to an employee, and we went through a whole rigmarole of looking at the flyer and trying to figure out what to do with the NZ app.
Eventually, she managed to find the coupon code from the back and just did it manually. So the NZ thing was a bust, but they are aware of the code so it does work. There also don't appear to be any restrictions on minimum price. I got Tetris Axis for $9.99 ($19.99 regular).
Also, SM3DL, MK7 and Mario Tennis are all on sale for $29.99 this week, so you should be able to get them for $19.99 this way. That's a pretty sweet deal.
TL;DR version: I got $10 off Tetris Axis so it was $9.99. the NZ app might not display the coupon, but they will be able to apply it manually.