As per usual. 
I agree with this point.
I agree that Iran will play role, but I also think the Saudis have just a big as stake in the matter as Iran does.
I also think that the domestic forces in Iraq are playing a large counter-balance to the influence of Iran in Iraq. That said, I agree that Iran still can make or break Iraq, so yea I will agree with your sentiment on the whole.
I am not sure this was the entire reason Ahmadinejad was elected. He ran on a very populist platform promising mostly domestic reform. While I agree the dynamic you laid out played a role, I am not sure it was the only factor.
I think regardless of this dynamic however, when we invaded Iraq, and Afghanistan, classified Iran as part of the "Axis of Evil" and started saber rattling Iran was going to react much in the way they have regardless of previously discussions. Add all this to the oil price spike, the rapidly expanding problems in Iran, and I think we still have the same problem.
Russia has a vested interest in not seeing a nuclear Iran yes, but Iran flatly rejected the Russian offer on their nuclear program as well. Russia, in my view, and Iran, are connected by energy and arms sales. Russia is happy about the prolonging the crisis with Iran so that they can sell Iran arms. They are not overly happy about a nuclear Iran, but they know they will not be the target of a nuclear Iran. At the same time, by prolonging the crisis, Russia gets better energy prices, energy deals with Iran, and makes a bundle selling Iran arms.
I do not think Russia was the key to our Iranian relationship. Iran helped us for awhile in Afghanistan before it became apparent they would be on the invasion list.
I maintain that the threat posed to Europe by a nuclear Iran and the negative effect backing off of our nuclear and conventional deterrent to Europe (and Israel) would be a foreign policy disaster.
I am not willing to back off of this stance to a resurgent Russia that quite frankly hates the United States to begin with. We must maintain our deterrent to our allies and we must enhance and fund missile defense.
We need missile defense not only to offer a deterrent to Europe against Iran, but also for us against Russian expansion. Missile defense is the right way to go in my view, and backing off of our extended deterrent to Poland (as Obama is doing) is not only a disaster for the United States, but our credibility with our allies all around the world, especially after selling out Georgia.
