I think if someone were to make facebook in it's first ~2 years and keep it very basic it we would be good to go. The only features you need are: a profile picture, a wall, chat, and events.
In other words - a photo of yourself, a way of publicly messaging, a way of privately messaging, and a way to coordinate social events.
What else do you need for a 'social network?'
I would pay $1/mo for that. The simpler the better.