I'm actually surprised at how popular the game seems to be. Supposedly it's one of the best selling 3DS games in Japan, even outselling games like Super Mario 3D Land, Mario Kart 7 and even Legend of Zelda: Ocarina of Time 3D. In the US, it's behind many of the Mario franchise games, but it's still outselling the Pokemon franchise and 3D Zelda. No idea how the most recent Zelda game will change the rankings, but New Leaf is currently the 4th best-selling Nintendo 3DS game:
Hopefully, that means we'll be getting an even bigger version of the game on the Wii U pretty soon. Then I'd actually have an incentive to buy a Wii U.
Also, even though I live in a small farming town, with a population of about 4000, I've still managed to exchange Streetpass data with 6 other people playing this game just by keeping my 3DS in the car while going about my daily routine. I'm sure most of them are young kids, because most of the results I get are around fast food places like McDonalds or Dairy Queen (where I work right now). But, judging by the size of their houses, many of them appear to have been playing for several months now. So, it's definitely worth keeping Streetpass running at all times while playing this game.
Maybe I could get more results if I drove around schools and playgrounds… but, I could see that backfiring pretty quickly: "Honest, officer, I'm not a drug-dealer or a pedophile, I'm just trying to get Streetpass data for my Animal Crossing town."