Do I hear the faint whispers of a Third Party in the snow-capped distance?
You don't need a third party if you can subvert one or the other.
Defeating RINOs and promoting DINOs can advance conservatism greatly. That's Palin's strategy.
Some people are really attached to labels. A co-worker of mine, a self proclaimed 'conservative / libertarian', descends from union DNA, and votes Democrat no matter what the candidate believes in. He'd be thrilled to vote for a pro-gun, pro-life, pro-military and lower taxes Democrat, and so would his entire family.
May as well subvert and neutralize the brand names, since getting people to think and act for themselves is considerably harder. A new party would require a lot of new thinking on the part of people who clearly aren't inclined to do so.