I'd agree that third parties are generally a bad idea, but Medved oversells his case.
Wikipedia tells us that in the 1854 elections the most seats were won by the "Opposition Party," which wasn't really a party at all. They were all the candidates opposed to the Democrats. Although they won the most seats, they didn't control Congress because they weren't organized. The Republicans probably were a third party at that time after the Democrats and the American (or "Know Nothing") Party.
I don't know what kind of a lesson you can draw from that, but far from discrediting ideas, third parties helped to make them respectable. Those ideas, from abolition of slavery to prohibition to direct election of Senators to women's suffrage to deficit reduction may not always have been good ideas in themselves, but third parties didn't hurt such causes.
Medved does have a point, though: if your ideas already are up for discussion, it probably isn't a good idea to form a break-away party. You only lessen your influence.