Well, you got to figure what this would mean. The Iranian Socialist Republic provided critical support to the emerging Afghan Socialist Republic (which was a matter of degrees and increasing influence, not a all-or nothing affair.)
Of course, this means that the USA's good friend in the Region, Saddam Hussein, is probably more on his own. Saddam's annexation of Kuwait in 1990 would not have been "an acceptable arrangement" for NATO without his long-standing alliance with the Western Powers. Figure that Saddam probably needs to play a very different game without the USA's massive support.
The effects of this are hard to overstate--Iran is a Shia country, which has a historical grievence against the Sunni branch of Islam. Without the Soviets essentially choosing sides, the Sunni faction would probably be less tolerant of the USA. No troops in Saudi Arabia, for example.
Of course, we remember that the Iranian Socialist Republic was one more piece of the Soviet Union that essentially broke away from the Soviet Union shortly after the annexation of Kuwait. Still chummy with the Russians and their Afghan friends.
I'll say this much though--that Osama Bin Laden guy who caused all manner of terrorism in Iran and Afghanistan against the socialist governments OTL, he'd be looking at us right now if Iran didn't raise the red flag.