Just a couple quick thoughts, I'll try to say more later. Note that I only watched the english debate, as my french isn't good enough to gain anything out of the french one.

I don't think Elizabeth May did that badly really. I agree with your assessment that Dion didn't do particularly well. Harper came out of it looking somewhat sympathetic, as the bulk of the debate was the other 4 leaders gangbanging him, and as you said, he came off as really polite. Layton seemed to want to hit some points repeatedly, and I recall him stumbling a bit when the moderator asked him for specifics on the art funding issue.