I think Sepah (Iran's Revolutionary Guards) and Hizbullah probably do want nuclear weapons simply for the prestige and fear they generate--if nothing else. But Israel having nuclear weapons certainly feeds that desire. And Israel's nuclear threat is used by Iran's regime in their effort to rally support.
Getting Israel to sign the non-proliferation treaty could erode what popular support remains in Iran for the brutality exhibited by Sepah and military Basij under Supreme Leader Khameini on behalf of alleged President Ahmadinejad. And since support for them also entails financial support for Hizbollah, Israel should recognize that joining the NPT could help erode financial and popular support for Hizbullah.
If this could also be explained to low income people in Iran who are benefiting from improvements and handouts from the Ahmadinejad administration, despite his mishandling of the economic issues--which has contributed to unemployment and inflation--and if the general public in Iran could see the Israeli bogeyman reduced so that less money seemed to be needed for defense, they might sigh a collective sigh of relief. Iranians have a lot of economic problems at home that need to be dealt with. Friends in Iran (including Muslims) have told me they would prefer that Iran's wealth benefit the citizens of Iran and their quality of life rather than be spent on Islamic hardline militants.
(I wrote this in response to Reza Aslan's "Stop Talking Down to Iran" in the Daily Beast.)