Why didn't he do a kamikaze run at the Narada rather than risk having Red Matter fall into Nero's hands?
I'd argue the exact opposite - essentially, that the movie was too short because the obvious was overlooked.
That is, I see no way for Spock to evade Nero's tractor beams or achieve ramming when tractored. The Vulcan's tiny ship shouldn't have a prayer against the asteroid-towing beams of the mining rig. Thus, the ramming attack at the end of the movie should have utterly failed, and Starfleet would have to have devised another means to bring down the clumsy but surprisingly resilient behemoth.
The final scene: Kirk getting promoted and decorated. In the background, Starfleet admirals whisper: "Isn't this a bit premature?" "Well, yes, sort of. But we have been bombarding that ship for three months straight now, and while the Romulan bastard is cornered and helpless, he's not giving up any time soon. I for one am tired of waiting it out."