Animal Crossing is terribly addictive so I certainly wouldn't sell it to yourself on that basis. What I've found is when they start exploring "free" things, it's time to put the thing away. They are bored and don't know it and that's your time to start parenting rather than letting the machine do it for you.

I tend to encourage my kids to do something in the real world when this happens. They still paint, draw and read and it's a welcome diversion after a few minutes away.