Plame and Wilson were paid (by Iraq) to write a critical report that would discourage Bush's war effort and the whole Karl Rove situation is a diversion. Others are involved.
Ok...but it would make a good movie!!! ;)
To be honest, I have a simpler theory: Plame was among many government operatives left over from the Clinton administration who cooked the intelligence due to either incompetence or outright political and personal hatred of Bush to make it look like Iraq had more than it did. When someone actually decided to go look for evidence, Plame got her husband on the team to Niger in order to deflect everyone away from her own incompetence or motives.
Alternatively, she shared her husband's view of the war and the current administration, and got her husband on the team to help Niger officials destroy evidence and cover up their collusion with Iraq.