I totally disagree. A superstar is precisely what Romney needs because he's so boring. And McCain did not lose because Palin outshone him. He lost in part because Palin turned off tons of moderates and independents because she came across, rightly or wrongly, as a no-nothing yahoo in large part due to the left-wing media's hachet jobs on her.
It's true that people rarely vote for a presidential candidate solely because they like the running mate, but a great running mate can really help. And a poor choice can hurt. Romney is a milquetoast. A snazzy running mate like Rubio, especially since he's Latino, is a great idea.