Hearing Nader talk makes me think there's exactly one reason he's running for President: because he wants to be President. I can't tell if he honestly is so dense that he doesn't know he has no chance, but given his absolute disdain for both the Democrats and Republicans, and given his seemingly enormous ego, I personally think he believes that it's his God-given right to be President of the United States, so much so that he'd accept help to further his campaign even from a party that he despises.
Maybe I'm wrong and maybe I just have too low an opinion of Nader. I doubt it, though.
I have a feeling you're right on about Nader's motives. I also predict he will recieve far less votes this election than in the last one. I'd expect Badnarik and Peroutka to make a bigger impact (combined).