I agree with you that Iran has greately benifited from U.S. invasion and toppling of two hostile regimes to its east and west. I think there are patterns that exist where both U.S. and Iranian interest are common, and no doubt they may be more ammeanable to Shia influence than what they consider to be anti-Western/American discordant/inflexable sunni rather. But in my view in Afghanistan that might be a case, but nevertheless U.S. is bound to make concession to the Iranians given their vulnrabilty there. I think once, according to them, Afghanistan consolidated and there is a pro-American government, they could give a rat about Iran. On the other hand, in my view other than demanding share for its Shias in Afghanistan on many levels strategically both the U.S. and Iranian interest are bound to collide given both countries' long term interests. I doubt American invasion of Afghanistan and Iraq was a concerted effort with Iran, yes there might be overlaping interests.