Here's the problem: Israel will also have to take out Syria's (and Saddam's) WMD and find a way to check-mate Pakistan from sending over a sympathy nuke. That Lebanon will be turned to glass goes without saying. There are no half measures.
Another issue I forgot to mention is that if Israel strikes Iran all of Israel’s enemies will come to Iran’s defense, it would be World War III. I think Israel is fully aware that they will get zero support from the United States(Especially under Obama) so its up to them to defend themselves. If they think Romney will win they will hold back on attacking Iran, if they have info that Obama will win they will go ahead and do it