The most original insight I've encountered on Kerry's speech was something I heard in the car this morning, one of the commentators on the Diane Rehm show, who said that Kerry's speech was set up to portray him as a sort of national daddy, the steady calm presence presiding over a bunch of smaller, noisier figures. This plays to his strengths, and even harnesses his physical size, as he towered over John Edwards.
It's an interesting thought. Alas, I have no idea who was speaking, whether it was James Fallows, Stephen Hayes, or Frank Sesno. I doubt it was Hayes, though.