IMHO Iran wants Nukes because it wants to be safe. Yes I agree that the sheer stupidity of some of their leaders regarding Israel means that we are wary of them. If you look at it from their point of view you can imagine how they feel. The West have been meddling in Iran for some time now, even to the point of being complicit in overthrowing a government and replacing a leader with a puppet.
In addition to this, it is bordered on both sides by countries with whom it has either been at war or has been occupied by troops of countries who are blockading it economically. There have been numerous threats and rumours of attacks by other countries against its facilities and indeed, the stuxtnet attacks which crippled their reactors. Lets not forget that Obama himself said that such attacks on the USA would be considered an act of war.
Now of course things are slightly different. There is a new leader in power who even tweeted greetings and congratulations to Israel on its last holiday.
I don't believe Iran, one of the oldest civilisations in the world would seriously attack Israel unless the country and its leaders had a death wish. In order for Iran to be completely safe from a perceived attack, they would like a nuclear weapon, if only to give them a bargaining chip, just as North Korea has done.