they get no benefit from using them. most of the anti-usa, anti-israel stuff is simply part of the internal politics of the country. unfortunately for the mullahs, the crazed, militant part of their populace that eats up the anti-west rhetoric for dinner has been swamped by the more progressive children of the revolution in a vast population explosion. the mullahs keep screaming 'down with the usa' but the population (ESPECIALLY in tehran) is increasingly pro-west. i would guess that most mullahs are of the corrupt, self preserving variety than the overly religious, islamic jihad driven type. many iranians i know seem to have this opinion. the real religious types arent in tehran anyway, they seem to hang out in 'religious' cities like qom where they are surrounded by like minded angry young muslims. i sometimes read people here calling for nuking tehran, but thats wrong. tehran is the last place you would want to nuke in iran, because thats the pro-west heartland.
still, despite my beliefs here, who wants to take the risk? im all for bombing the reactors, but it needs to be done cleanly. we shouldnt risk the great asset that is the pro-western feeling among iranians.
hmmm, just to be more clear about answering your question, the mullahs on balance, are more concerned about their own power, self preservation, and regional influence after that. nukes give them power, but as soon as they use them, its all over. what the nukes gives them, once they have them, is immunity from invasion. and they KNOW about invasions.