AND ANOTHER THING while I think about it, on the subject of the Decline phase of a community website's lifecycle, which can be characterized as either Sustainable Cosiness or Tragic Heartbreak depending on whether or not the people who are there actually want to be there:
If you're ever on a website and you find yourself thinking "Man, this website's culture is super toxic, I'd better increase my involvement so as to provide a good example and thereby improve it," then CHRIST JUST RUN