re: Would Iran still be a threat to us if we stopped meddling in the ME?

OP I'm with you, to some extent. I think the threat from Iran is overblown in a dramatic, major strike sense and that the fanaticism is largely overstated.

Candidly, I think there is a very good chance that part of Iran's basis in funding and supporting a variety of anti-Western and anti-Israeli terror causes is to provide a steady trickle of motivation for Western intervention in MENA and thereby propping up the occident-orient battle Iran needs to maintain the status quo as the sunni states steadily modernize (relatively).

That said, I think a lot of the disconnect is because the public and the IC may speak a different language on this stuff. Iran isn't likely to pick an existentialist fight with the US. They're not, in my opinion, constantly looking for opportunities to strike a massive blow to the United States.

Their tentacles are everywhere, however, and in that sense they rightfully garner a lot of military/intelligence attention. And while it's easy for me to look at Iran's population, the history of how radical Shia groups have operated and so forth and conclude Iran probably isn't worth losing sleep over, it's hard to blame the military/IC/political class for not putting all their confidence in that type of conclusion and operating instead on what they see - which is Iran consistently sticking its finger in our eye.