How much pain is the "Vote, even though it helps the Republicans" faction willing to put the country through? How much sacrifice? It's the problem of third parties in America that to establish themselves, they have to allow their opponents to win. By the time a new progressive party established itself in the current electoral regime, the Republicans would have held power for at least a decade--that is, if the NPP's members were allowed the vote by the end of that time. But it is more likely long before that time, the hopeful third party would have fallen apart.
I think we'd do better to work for electoral reform, and hope that the Zombie Party falls over from a deficit of brains. Maybe we can give it a push.