Third parties aren't really an option in our winner take all (non parliamentary) form of government. (see CGP Grey, who I think explains it best/with the cutest animals: https://www.youtube.com/watch?v=s7tWHJfhiyo)
For better or for worse, it's usually better for the parties to absorb new ideas that are gaining traction among their constituents, rather than have the votes cannibalized and spoil the election. In the most recent case of this Republicans + Tea Party, this was a huge boon for the third party, as I'm pretty sure that they'd still be a fringe group with mostly local influence rather than a large portion of the House, and a smaller, but relevant, part of the Senate. It's clear that it's going less well for the establishment Republican brand, but if they had stood firm against the Tea Party, they probably would have lost a bunch of elections. They're still officially in power, which is probably better for them than the Democrats in power.
It really doesn't matter how many people are disenfranchised with the system. Unless you change how representatives are elected, you will still eventually trend back to a two party system. imo, your best bet is to change the party you are most aligned with from the inside.