Hmm. I considered trying to do a scaling mod for lifespan like that, but then realized that A: Sims would effectively live forever, and B: Everything would become more trivially easy than before.
Yes/no...I play a strict rotation and it seems to work fairly well so far. "So far", of course, is the weasel-word. I can see a time when I won't care much about certain families, and I realize that unplayed is forever young from the perspective of the neighbourhood, but I am already working toward that day. I am making sure that my current crop of townies are ageing along with my playables. I have all the no regen corrections installed, and when I have sims that just don't interest me enough that I want to play them, I plan on sending them off to become new townies and live their own untrammelled little imaginary lives.
In the meantime, I do have to work at not making things too easy--hence my draconian standards on skilling and my use of syberspunk's excellent harder, harder grades hack. It's a slow process, but I'm also altering all the careers and installing many more--dead end jobs that never pay well, and desirable jobs with glass ceilings that my sims will only be able to shatter through 2-5% chance cards, with neutral, bad, bad, good results.