Yep I am also in the same boat.
Over the time I learned that best approach is to have all of them in the same save. Sometimes i revisit later, sometimes I incorporate them into my new story. And because I have some history with them I like them over time even more. If I for some reason want to/need to restart whole save I actually copy all of the families and sims I like the most to my new save and just continue. I will turn off aging for everyone but my current family or sims who are directly participating in the story.
The other thing to keep me interested is to make several goals and challenges for my sim stories. I take existing challenges and tweak the rules to my liking, sometimes I even combine them together. For example teen runaway + rags to riches + legacy challenge.
