If Toomey wins while Trump loses, is it still fool's gold? That seems to be the likely situation right now (though I prefer the reverse.) It would show the GOP can win something here during a Presidential year. (I'm curious if the AG race might be tilt R too. Lots of semi-informed people still mad as heck about Kathleen Kane for whatever reason, but the uninformed will surely be filling in nearly straight ticket ballots for both sides.)
Incumbency can skew things (though it's not always enough, apologies to Santorum).
Of course it can, but a relatively low turnout election that was won by just 2% isn't a great advantage. Most people who didn't vote in 2010 probably don't know who Toomey is, and we are talking about 40-50% higher turnout. A rematch really ought to be starting with Sestak favored, but it doesn't appear that way for the moment.
The people also just rejected Corbett in a landslide when he was not that much worse than any other Republican in this nation. For any GOPer to win in an election year would be quite a feat - incumbent or not.