Let's just go back to 2002 and think about what Iran must have been thinking during the U.S. preparations for the invasion of Iraq. If someone had approached the Iranian government and suggested that within five years the following conditions would be in place . . .
1. Iraq's Ba'athist government overthrown
2. Saddam Hussein executed
3. A new Shi'ite-dominated government in place in Iraq
4. The U.S. utterly incapable of mounting a serious military campaign anywhere in the Middle East
5. The ruling party in the U.S. government thrown out of office
6. Iran's biggest export (oil) trading at historic high prices
. . . I suspect nobody in Iran's government would have believed you. They couldn't have done any better if they had placed their own agents in position of power in the U.S. government.
If you haven't read it, you might find America's Secret War: Inside the Hidden Worldwide Struggle Between America and Its Enemies, by George Friedman, founder of STRATFOR, helpful. Although some of it might be outdated already - and STRATFOR has to stay current because that is their business - it was one of the more insightful works to be published about the Bush Administration's longterm objectives and goals in the Middle East.
Late to the discussion.
Although I did and still do support the removal of Saddam from power, I often feel the action may have been a stategic blunder. Iraq under Saddam did pose a threat to Iran based on past history, and such a threat may well have
pre-occupied Iran and kept them from going down their current path.