I re-start very often. Usually, when I return to the Sims from a hiatus, even if I intend to play the same family, I still delete the current one and start from scratch. It's just a personal preference of mine. I have a story to tell, and everytime, I want to start it from the beginning, here is the family, here is their backstory, now let's build a life for them. And if it decides to go in a different direction this time, then so be ia Also when I create a completely new family, I send them into my new save, and take it from there. I like to keep my focus on 1-4 families per save, usually.
I think I keep one really old save since the beginning though. It serves as the experimental save for all my untested whims and idea I don't want to bring into one of my played saves until I've seen the result.