I offer my answer in this piece. Here's a sliver:
The functional reasons are compelling: You don’t want your organization to dissolve because your leadership gets sandbagged, or because your information system is way too top down. But function and form is just one reason the Tea Party should never formalize...
A formal (hierarchical) organization - like a political party - is not only too centralized, but it becomes less effective as a check on government power. Currently, the Tea Party is coalescing around anti-incumbent, anti-elite and anti-state-power themes. It moves from without and, due to it’s form, is not as corruptible. Don’t believe me? Try lobbying the Tea Party.
There are trade offs, of course. What you lose when you’re decentralized is decision-making power, carried out at some instance, based on some plan. You can’t just turn, go straight, or back up on a dime. Tim Kaine or Michael Steele can’t either, but they can turn the ship with commands and controls to a far greater degree. Their organizations are more like spiders.
But the pluralism and broad theme-orientation of the Tea Party makes it effective in ways that really count: like keeping politicians accountable, raising a stink, and getting people to the polls--which is currently the only game in town when it comes to checking Leviathan.