I think this really shows that Santorum shouldn't be the nominee. He performs worse in his home state than Romney. Romney won't win, but he'll come closer than Santorum would.
Oh, ok so based on that logic, the selling point is: "Romney will waste more of our money on a state he won't win." Great!
You still have a downballot effect. When the MI GOP decided to take their inner feud public and released that McCain was dropping his active campaign in Michigan, people stayed home because they didn't care anymore, and I think that led to Tim Walberg losing his Congressional seat. Thankfully he won it back in 2010, but when you have a weak top candidate, downballot races suffer.