We still don't know for sure what Nero's plot is. It's assumed he's trying to kill Kirk, but there's been nothing explicitly saying that. They have said, though that the movie is Spock-centric. I just think a movie about a baddie flying through time to kill someone who's already dead seems kind of pointless. Why not have him be Spock's son, an idealist like his father, who is on the polar opposite side of the Reunification issue? This would give him the motivation to go back and attempt to toy with his father in the past, possibly changing his outlook on the reunification issue 100 years before the movement is even started.
