Posted By:
E, DanielNicely laid out.
I'll paypal my dues (not more than $20 i hope 
) the minute such an organization is running.
It's been asked to what purpose an umbrella association serves?
As all such groups, it serves like-minded peoples.
Why does it work? Because people buy into it, literally.
If the ideals are such that they speak to you, and the principles are those you would like to practice and have practiced with other hobbyists/members, then it works. Organizations exist because of the very natural inclination to join like minded peoples to share common passions or interests, or because of inherent inequality in power structures especially concerning health and safety.
If you get the basics right and keeping it simple as David has laid out, then it works. You don't need to chase people to join as much as allow the concept and idea to marinate amongst hobbyists, and it will draw similar minded people, some of them the 'big players' who will add interest and a percieved legitimacy of concept. And over time, if the concept has been well worked and is honestly good, the sheer weight of opinion will encourage the community to a greater extent to want to be a part of it.
And why will it affect practices?
Because those who join will want it to. Those whose activities are deemed inappropriate for the community will find themselves outside of their niche, or cash cow. I truly believe in almost every way it will be self policing, and where clear fraud has been committed the legal system can be used to correct the wrongs, and where the activity simply blurrs the principles of the association, that person can be excluded from membership.
I sure as heck know that I would search first, buy happiest, and sell most comfortably to people who shared at least my basic understanding of reasonably appropriate behavior in the hobby.
Daniel