I believe it’s worth refining the association option a bit further and taking the professional association model as a guide. One thing that distinguishes professional associations from unions and a lot of other collections of people is that they have codes of ethics. A way people are expected to behave or not behave as the case may be.

In suggesting a bloggers/podcasters/etc code of ethics I am immediately aware that I probably don’t want the pain of being on a drafting committee! Nevertheless, a code that avoided being too specific could set a standard of “how we do things around here”, unless of course the association decided to be so open as to have no qualms about, for example, becoming a happy hunting ground for spammers and post scraping plagiarists, for instance. A code of ethics or code of practice might also give some comfort to those bigger spenders you envisage ante-ing up for a more influential role.

I emphasize that the code should not be too specific or detailed. One very good reason for keeping it general is so as not to waste time on trivial arguments or give too much airtime to nit-picking debates.

Or you could use the nightclub bouncer approach and have someone appointed to exercise totally arbitrary, subjective judgement about who should be allowed in and who should not, or should be ejected without recourse to any other authority. I say “someone” because a committee of one would be the most effective approach for this option.