Hmm, this reminds me of Asimov's Robots/Empire/Foundation universe.
In this universe, before the events of Foundation, there are two main waves of human expansion. During the first, humans populate and terraform a few dozen planets. By tightly regulating their man-made planets, automating everything, and having excessively tight import restrictions, they live better lives than those packed in on Earth. Their lifespans increase dramatically, and their birth rates drop to sustenance levels. These factors create a strong cultural divide between them and the humans who are still on Earth.
Eventually the humans on Earth get their act together and begin expanding throughout the galaxy again. This time however they do it quick and dirty. Short lives, lots of kids. Their population growth remains unbounded while the initial wave of human settlers becomes increasingly isolationist. Eventually the people and worlds in the first wave of expansion are forgotten.
