Not much
The evidence proves that the sanctions were working. And perhaps, today, we might have the political will and international support to keep Iran from producing nuclear weapons - something Saddam Hussein wan't even close to producing. Saddam's best missile had a range 129 miles. Iran's newly developed missiles can reach the heart of Europe. How soon before they put a nuclear warhead on top of one of those babies?
The war in Iraq has been one of the worst foreign policy decision made in modern history. We are going to be paying a price for that terrible judgement for years to come.