Is there a case for the default settting to 'Other Members of your Group' ?
I think there's a conflict between that idea and the fact that one's group profile defaults to the content of one's Account Profile. When you join a new group you might inadvertently expose things you would have changed had you had a chance to review the content of your profile in the new group before exposing it to the other members.
That's a particularly uphill battle for members who prefer to be "email only" and are reluctant to log into the site. I'm not sure there's anything to be done for them other than continued encouragement.
Members who do visit the group's pages could perhaps be given a reminder of some kind. But I wouldn't want it to be a constant nag - it would need an easy way to turn it off. Perhaps just visiting the Group Profile page could do that.