Are we stretched that thin? Or is that what the U.S. military would have are enemies in the region beleive...to bait them out, and have them play their hand on our terms. IMHO, are latest troop build up in Iraq and Afgahnistan...has more to do with Iran than any worries over insurgent attacks during the installment of the new Iraqi Constitution...but I am not at CENTCOM...so...that's merely a guess.
Plus-Iran is much smaller than Iraq...we have people prepositioned, and we'll be able to take a more "gloves off" approach to those jokers...
Well in terms of strength, if Iran is supplying the insurgency with weapons then an armed conflict would slow down the weapon smuggling and lighten up the burden on securing Iraq.
Probably what would work better is a couple covert operations into Iran to sabotage domestic control ops. Essentially do the exact same thing back to them. Take out a few communication centers... maybe a couple police stations... power relays. Just make the Iranian boot keeping the plebians under control a little lighter.
Two Mechanized divisions can make short work of Iran. A modern US division has nearly three times the firepower of Patton's WWII Third Army. They are smaller and the government has a population that hates them. They are ripe for overthrow.