You know, I think I'm looking for an answer to this very question myself.   I haven't yet joined an ATV club, but there is a likelihood that I might.  I tend to be a joiner, not a "lone biker of the apocalypse".  I've visited various club web sites and here are some of the things they have to offer:

• A club member is invited to participate in riding adventures on a monthly basis with others of similar interest.
• You can attend a monthly meeting and pay a nominal membership due.
• The club tries to keep you informed of recent rules and laws, what's open for riding and what's not.
• The influence the club brings to bare on available riding venues is actually more impressive than individuals in many instances.
• The Utah ATV Association has a social conscience.  They have an annual ride for Muscular Dystrophy. I've never seen a web site of any of the land closure advocates, that proposed doing anything for anyone but their cause.
• The club also promotes good citizenship amongst its members, suggesting responsible use of riding venues, and safety in riding practices.
• Service projects are also part of most clubs activities.  They have done work cleaning up sites like Five Mile Pass and Simpsons Springs.
• The clubs offers a means of selling off your old machine by advertising for you on the web site.
• The clubs also offers you a newsletter.

• My brother was a member of a Motorcycle club.  They were out on a tour with the club and my brother attempted a curve on a mountain road too fast.  That's all she wrote for my brother.  He was likely trying to keep up with the other riders.  It was a choice we've paid for ever since. It would have been nice if the other riders of the club in the front of the pack had just a bit more self restraint and consideration for the group.  It was their bad choice that affected someone else to make a bad choice.  They may have been able to handle the speed safely, but someone else could not.
• As much as I love recreation with ATVs, it is not a religion for me.  If some people want to go riding on "religious time" I suppose that is up to them.  I don't feel comfortable with that myself.  I already have a religion and I try to be dedicated to it.  I don't want or need another factor that would draw me away from what I consider to be most important in my life.
• One more meeting.  It always starts out simple as one more meeting, and before you know it, I'm in charge of something and it becomes something like a full time job, to do it right.  The perspective of home, family, job, church, politics and other diversions tends to get things pretty jammed with activities.  It is a matter of priorities isn't it.

I think the majority of ATV riders are not club members but are family and neighborhood riding associations.  That's how it has turned out for me.  I'm thinking of the possibility of forming my own club in order to share information with others on a regular basis.

Sometime it may be fun to have an ATV convention, where all the ATV enthusiasts can get together and share their experiences, ideas and get some education from our governmental and manufacturer experts.  Doug Miller's "outdoor expo" doesn't fill the bill.  I just hate to pay good money for the opportunity of having someone pitch their products at me.

In the final assessment, everyone has their choice.  Clubs with members that don't choose to contribute to the overall welfare of the group are doomed to failure.  Were I to actually lay down the money to join, like everything else I do, I'd try to be the best member I can be.