You can see the intellectual influence of the antiwar people in the speeches of Democrats opposing the conflicts in the Gulf in 1991 and Iraq in 2002. Their arguments are a better fit for the facts of the Gulf of Tonkin incident of 1964 than for the facts on the ground in 1991 and 2002.
Like the antiwar activists of 40 years ago, the tea partiers include many good citizens moved to political involvement because of intellectually serious concerns about public policy. Similarly, they include a much smaller number of cranks, conspiracy theorists and congenital malcontents.
Tea partiers have caused some internal party splits (see the New York 23 special election), and some may launch primary challenges or third-party efforts that will elect Democrats. Any time a large number of motivated people inject themselves into electoral politics, they cause a certain amount of chaos.
They also add a lot of energy, political creativity and enthusiasm into a moribund and dejected political party, like the Democrats of 1968 and the Republicans of 2008. New people change the positions and focus of their parties. The Democrats before 1968 were a pro-Cold War party. Since 1968 they have been, with occasional exceptions, a dovish party. Hawks need not apply (ask Joe Lieberman).
The Republicans for the last two decades have been a party whose litmus tests have been cultural issues, especially abortion. The tea partiers have helped to change their focus to issues of government overreach and spending. That may be a helpful pivot, given the emergence of a Millennial generation uncomfortable with crusading cultural conservatism.
It's not clear whether the tea partiers' influence on Republicans will last as long as the antiwar cohort's imprint on Democrats. But their concern -- the fact that government spending is on a trajectory to increase far beyond revenues -- seems likely to persist. In which case a spontaneous movement that no one predicted and that no one person led could end up, again, reshaping one of our great political parties.