I see your point here, but part of the effect of an insurgency (which carries a degree of wild enthusiasm that neither the Green Party nor the Libertarians have been able to muster) isn't just that its support makes people who would have voted one way vote a different way, it's that, especially at primaries, it can deluge the polls with so many voters who mightn't otherwise have gone as to effectively eliminate early any candidate who doesn't have their support. It might end up being the case that Tea Party endorsement becomes a prerequisite for gaining the Republican nomination for office in some states or locales, and even if it's split and so you're not guaranteed the nomination with TP support, you're absolutely guaranteed not to have a chance without it.