Some communities get too busy. Members can’t keep up. Members miss important debates, lose track of development and soon don't feel part of the community anymore.
The solution is to have a round-up of the week, and invite comments and participation. Time-restricted members can still be involved.
At the other end of the scale, some communities are too inactive. Little is happening, members aren't participating, there is no activity.
Start a weekly “What’s happening this coming week” mail out. Every Sunday, everyone gets a list of what’s happening the coming week. Of course, you need to plan things to happen. But, hey, that’s your job.