Personally, so far I see no justification for the reboot. This film ends with everyone back in the saddle to start the 5 year mission. In hindsight, NOTHING was at stake. Nobody of the main characters died, Vulcan's destruction is glossed over, and so forth.
They could have achieved the same by sticking to canon, telling interesting, character shaping stories for each of the main characters, like Kirk witnessing the massacre on Tarsus IV, or Kirk's time on the Farragut, and even invented some adventures that lead up to the 5-year mission.
The whole argument that you can't make exciting prequels unless you reboot is nonsense. The Star Wars prequels prove that. Heck, Harry Potter, Lord of the Rings and Hobbit prove that because two thirds of the audience already know everything that is going to happen because they read the goddamn books. And with the new Trek, two thirds of the targeted audience DON'T know what is going to happen, so the suspense is there.