I don't see why someone wouldn't just put their 3DS in a bag in which a 2DS fits fine as well.
If you're going to go outside, I'm betting that you cannot fit your 3ds, keys, phone and wallet (maybe headphones) in the same 2 pockets.
That's kind of easy. I do it if I'm visiting places. If at college then I carry the 3DS in my bag though.
Wallet and keys in one pocket, 3DS and phone in another. (I will admit that I have a small phone though).
Or another way is that, like a lot of people, you have your wallet in your back pocket and you have a whole pocket free for the 3DS.
Headphones, assuming they're the sort that sit on your head with a band over the top of it, then you can wear those around your neck or on your head. (Who carries them in their pocket?)
Earphones can just fit in any pocket since they're so small.
I think I would agree with snot that a 3DS is nicer for AC:NL on account of streetpass, which is also a bonus for a number of games.
On whether or not you should buy the console just for that game then that's up to you and how much you like the game.
If you really like it, then go for it.
And if you do have the 2DS/3DS then you can always keep an eye out for any cheap DS/3DS games out there that you might like to play. I didn't have a lot planned when I got my 3DS, other than anticipating the next Pokemon game to be 3DS only, but since then I've picked up a few additional games I wouldn't have considered, some physical copies and some digital.
