"Even assuming you're willing to discount Turkey, given it's history of cooperation during the Iraq War..."
I AM willing to discount Turkey as a threat to Iran's vital nat'l interests. Absolutely, yes. What cooperation do you speak of, by chance? Perhaps when they denied entry of the 4th Inf. Div. into Iraq through Turkey at the start of the war? Hmmm...
"...and the shared problem with Kurds,"
Yup. EVERYBODY, it seems, has a problem with the Kurds. Nothing special there. Both issues with Kurds and the presence of a N.A.T.O. Turkey long predate U.S. involvement in Desert Storm, much less OIF. Big deal. So, again, I ask you- How does the removal of Saddam and the baathists (playing soon at a bar near you
); eliminating the threat of Iraqi expansionist ambitions-twice proved in the last twenty-five years; eliminating any Iraq possession, use, and further future development of WMD; and alleviation of baathist persecution of Iraqi shias create a greater security threat to Iran?
"... they are still faced with US troops on the ground in three neighboring states and a vast fleet just off the coast."
Perhaps. However, N.A.T.O. is in Afghanistan because of OEF, not Iran. That's a fact. The U.S. Navy is in the Persian Gulf because the Iranians tried to once close the straits of Hormuz. Very, very bad Persians. That's a SAD fact brought upon themselves by their miscreant behavior.
So too, now, with Iraq. Were it not for Iran's interest in keeping America IN Iraq, on Iran's nefarious terms, we might well have been gone long ago. Chankya, you can't have it both ways.
"Are you saying that this does not constitute a real, credible and immediate threat to Iran(country and regime)?"
American forces constitute a real, credible, and immediate threat to damn near any nation on earth.
"The validity or otherwise of such a presence is besides the point."
The validity of U.S. forces in Iraq is precisely the point. Their presence is valid. As such, other neighbors of Iraq feel no such threat by our presence. Does Kuwait, Jordan, Turkey, and S.A. see our presence in Iraq as a threat to their nat'l interests? If so, where are their calls today for our immediate departure? Does Uzbekistan, Pakistan, and Tajikstan call for the immediate departure of N.A.T.O. from Afghanistan? Has even Iran done so? Those Persians Soooo loved mullah Omar and the fellas.
"The fact remains that today there is a visible and enveloping military presence by an openly hostile state."
Quit shipping VBIEDs, EFPs, sniper rifles, etc to Iraq. Quit training shia death squads. Quit interfering in Iraqi politics. Quit trying to de-stabilize the GCC states. Quit trying, most of all, to build a NUKE.
That explains your "visible and enveloping military presence". Iran is it's own worst enemy.