Taking a leaf from the business tree, it can be beneficial in developing local story guilds to understand the basic rationale as to why people associate with an organization. There is the obvious social aspect of being with other people. There is the shared interest aspect of finding people who also love storytelling and listening. There is also the status aspect that says I belong to this group and that makes me special (remember storytelling requires people to be able and willing to "show off"). Creative people often need positive reinforcement to affirm that they did well and this can be mistaken for arrogance and pride. The ego factor is a real element that has to be recognized. There is also the mission aspect of membership where the member is reinforced in helping the group achieve its mission and finding purpose in their life.
So, what does all of this mean? A successful group will provide a clear cut mission, opportunities to learn and share, and plenty of chances for the members to be showcased, highlighted, honored, and recognized. This will keep them coming back for more, make them eager to "re up" their dues, and ready to tackle leadership or volunteer roles with energy. Give members more bang for their buck and reap happy and productive members.