Cecil -
Seems to me that there are two issues. One, as Jim notes, is that being a member may obligate you to the gallery in some way - and you need to decide whether you can afford the time and other consiuderations that obligation entails.
But the otherissue is that being a member of the cooperative gallery assures you of being able to show in the gallery. OK - the upside of that is that you would have access to the gallery and could should your work. But there is also a downside - it can be argued that showing in a cooperative gallery is not the same as showing in other galleries for the simple reason that individuals who are not members of the cooperative cannot show their work, and the process for jurying working, if one exists at all, is subordinate to whether the artist is a member of the cooperative. That is, a cooperative gallery provides a venue to artists who can't get a gallery showing any other way.
The New York State Lottery currently is running a humorous TV commercial featuring a make-believe baseball team manager being interviewed by the press - the manager is asked about a player who is clearly incompetent, and he responds that he needs to be given more time to develop his style. A reporter then asks if it matters that that player, who apparently has won the lottery, has just bought the team, to which the manager responds "Next question". Likewise, being a member of a cooperative gallery sometimes has the connotation of being an way that dillitantes inflate their egos.
Obviously, I don't know the specifics of the cooperative gallery you are considering, but you might want to think whether that involvement would be viewed as a positive or negative factor if you were seeking representation by commercial galleries in a major city.