Anything based on the SCUD, and especially a stretched or multi-stage design, is going to have some pretty significant problems. The SCUD is really little more than a V-2 with a slightly improved guidance set and higher performance fuel. There are some inherent flaws in the design (the use of eroding jet vanes, non-detaching RV, et cetera) which severely limit its accuracy even at nominal ranges, and as the Iraqis discovered with the SCUD-derived al-Hussein missile.
Personally, I’d be far more concerned about terrain-following long range cruise missiles, and especially those capable of sea launch. This was once the domain of superpowers, but with commerically available avionics, inertial laser gyro guidance, and GPS/GLONASS/COMPASS/Galileo system you can acheive far higher accuracy than an unguided ballistic RV. Iran has been working on cruise missiles based upon sea-skimming Russian and Chinese supercruise designs, and these are, in my opinion, a far greater threat than notoriously inaccurace SCUDS.
I think Iran certainly has a strong motive to pursue nuclear weapons. Just look at how the US has dealt with the other two putative “members” of the “Axis of Evil.” The one without nukes gets invaded. The one with nukes gets food shipments and negotiated terms. The object lesson is that nukes=respect.
(Note: I am not defending the despicable Iranian regime; just pointing out its motivations. Wouldn’t you seek nukes if you were running the place?)