There’s a world of difference between Palin and Santorum. Santorum is a go-along, get-along big-government type, and Palin has a history of actually cutting AK’s state budget, building its economy and state balances, ethics reform, etc..
Also, though Palin is solidly pro-life, she doesn’t have Santorum’s weird penchant for denouncing contraception, suggesting gay sex should be illegal, etc..
One is the leader of the tea party movement, the other is the antithesis of the tea party movement.