Though history will probably record that Iraq possessed few non-conventional weapons, it will also confirm that every major power in the world believed otherwise and that Hussein’s goal was to re-establish WMD programs once the sanctions lapsed. Had the US and its allies not invaded Iraq, Saddam Hussein would probably have achieved nuclear weapons before Iran, and it takes little imagination to envision what the presence a nuclear Iraq would have done to the Middle East.
History will show that most major powers thought that Saddam had retained some chemical and biological weapons from his war with Iran in the 1980's, but almost no one other than the United States believed that he was actively pursuing WMD in 2002 or that the available intelligence warranted an invasion. Moreover, most major powers believed that Saddam had not taken any steps to reconstitute his nuclear program since the first gulf war.
If Iraq becomes the kind of secular democracy that we would love to see in the Middle East, Bush's standing will surely rise. However, I don't think it likely that we will learn anything that makes his original case for war look any better. In fact, history may well find the smoking gun that shows that the administration knew that its case was full of holes.