I think you are close to the truth. Wilson's story about Niger changed (according to the Intelligence Committee report) and outing Plame as revenge is really a lame accusation. The President getting revenge by revealing Plame's identity is really a pitiful sort of revenge, isn't it? I mean, what sort of revenge is it that gets someone a 6-figure book deal and appearances on all the political talk shows? I have never understood why anyone believed this was a deliberate attempt at revenge, anyway!
"outing Plame as revenge is really a lame accusation."
It is a lame accusation. And it seems to suggest desperation on Joe Wilson's part. As if he wanted to shift the focus from his wife sending him to Niger to imagined evil-doing by the White House.