I think there should be a minimum. It would weed out some of the people that are just looking to quickly earn some points. After all, isn't this site about giving thoughtful and honest answers to help people? It seems like that's changed.
If there was, I don't think people would be answering questions as often. Especially, if it takes up time and god knows no one likes putting in effort. And plus, if they did, it'll just be an answer full of unnecessary bs just to fulfill or meet the guidelines. Also, you have to take into account how many characters are we talking? 20? That's durable..50+? Hell no