won't be too much of a problem if it drops nothing but food and rewards no exp/coin...
sure, they can sell the food, but.... it will net at most a few hundred thousand coin for 24 hours of sweep. That'd be something...

I won't mind if they allow us to do instance with no reward whatsoever but can earn additional ninja stars. There are times when I can't pass the blue fight and have to go back later to get the 3 star, it's not really a fight I want to spend stamina on thou.