I think I've done and seen everything in ACNL, minus 100% catalog and badges. Someone please prove me wrong. Right now the only thing keeping this game from being repetitive is the online, for me...
Remake your town so it's seasonal. I remake my town to fit its season and reupload it to the Dream Suite. It sounds time consuming, but it'll keep you occupied! It's actually pretty fun.
If your town doesn't have a theme to it i would say work on that if that kind of idea interests you. Or maybe make a second character if you haven't already and turn their house into a store/mall. My second character will have a mall in their house and only the caf? is complete so far. Keeps me busy on top of my villager pic collection
Your can remake your town's decoration, get new villagers (if you don't mind that), redecorate villager's house or your own house, visit dream towns, make it a goal to meet all the villagers in the game... I don't know, I think it depends on what you enjoy doing in the game.