I agree, Iran is a real threat, but the political situation in Iran is quite different than Saddam's pre-war Iraq. Saddam was never faced with large numbers of pro-western, anti-authoritarians as exist in Iran. I think the US state department believes Iran could actually change via a combination of international pressure and covert support through the Iraq/Iran border. Why do you think Iraq is so hell bent in disrupting the new Iraqi govt anyway?
We gave Saddam a good long time to reform under sanctions. He never did. Iran is worth a shot.
The biggest problem is really Russia. They're deep in bed with the Iranian regime and no one has got the balls to tell Putin to back off.