Ringers will also bring their fans with them to different communities that they join. Ringers tend to be passionate, well-versed in the rules of debate, and very savvy regarding online protocol. They sometimes build lists or communities and hand them off to other members. They can be beneficial for your list. They will also be able to give you hints about what other list owners are doing, and what is working on other lists.
Ringers have incredible amounts of experience with online communities and lists.
Tap into it. And they will leave. I have followed ringer friends through a handful of communities and lists that they have started and left or shut down. Change is the norm for ringers, and they leave for a million reasons. You'll never make them completely happy, so don't bother trying.