"...and too much will be made of likability." Noonan makes good points here, but I think she dances around the obvious. While pointing out the inherent advantages of the incumbent in this process she misses the real task at hand; the challenger has the unenviable task of looking more presidential than the president.
If we go back to the beginning and work forward:
1960: Kennedy simply looked better than Nixon on TV and that was enough to look more presidential(you could argue as VP, Nixon played the "incumbent role").
1976: Gerald Ford ceded the "presidential look" to challenger Jimmy Carter with this moment:
1980: Many feel in one debate performance Ronald Reagan looked more presidential than Jimmy Carter. Here is 8:17 minutes of solid gold:
1992: Who can forget George H.W. Bush's "watch the watch" moment.
There are more, but you get the point. Noonan is right though. Romney doesn't need to exude likability. He needs to exude trust. Obama has built in trust to be president, as Noonan points out, because he is president. Romney's task is to look more presidential than the man who has the job now.