I'm sure people will still play it for nostalgia purposes. I never had it, so I'm not really interested in getting it. I tried going backwards to WW after CF and it just didn't work out. And I'm sure every now and again someone somewhere will stumble upon a used copy and the world will have a new AC addict.
I'll defiantly still play it. So far it's been the only animal crossing game that's kept me interested since I got it. I don't see myself playing it as much as new leaf but that is only because new leaf is portable.
I've never had Population Growing, but WW and LGTTC never got me back into AC. After I had seen all of the NL screenshots, I was super excited and these games were nothing compared to it. I'll be playing AC:NL forever when it comes out.
I still play the original and I probably still will after New Leaf is released. So far, no game has had better villager interaction than the original and that's why I keep going back to play it. New Leaf's villager interaction looks promising, though.