Since we are talking about boots on the ground, lets look at the middle east topographic map.
All that stuff you see around Iran are mountains and pretty tall ones at that. Meanwhile the arab states for most parts are flat. Iran can easily attack them but they cannot so easily attack Iran. You can also see why places like Iraq are so easily invaded. Just look at all that flat land. Then you see all those mountains in Yemen, no wonder its such a pain to deal with.
The reason they are trying so hard to start some internal uprising in Iran is because just looking at this map, marching in troops conventionally looks like utter pain. And I haven't even gotten into the part where assuming they got in, how they would have the logistics to resupply long term.
That why foreigner conquerors in the past waiting until Iran was in huge decline and had a lot of infighting before making a move. Only then could you take it piece by piece. And what guys like Alexander or Mongols did is live off the land which for nomads at least is very easy since thats their lifestyle. Today you are not getting fuel for the M1 Abrams living off the land in some mountain village.
While I do think US could get something out of it, its gonna be rather painful.