What do you think sanctions will do?
For Saddam they merely entrenched his leadership, with billions of dollars flowing to the government in question through bribes - in no small part from the Australian Wheat Board - in the case of Iran sanctions would put oil past 100 dollars a barrel and wouldn't stop the regime getting weapons.
The world needs Iranian oil too much for sanctions - it would never get through the security council, not in a million years.
Iran will get weapons, the higher ups running the country wouldn't let them be used for instant death rather as leverage - but they will spread, and sooner or later they will fall into the hands of those that would use them, I don't imagine that the "World of Islam" would fare too well in that scenario (I am of course refering to the Rafsanjani quote ~ if there was a full blown nuclear exchange between Islamic states and the West it would be loose and slightly less loose).
A nuclear Iran has some benefits, it will force alternative energy sources and make existing reserves viable, it may also encourage exploration.