[What would victory look like if we were to achieve it? How will we achieve that victory? What resources are required? Is the national sacrifice worth the goal defined in the strategy?]
Good questions. If we examine all the wars in which the United States has engaged and we compare the ones with successful outcomes to the ones with unsuccessful outcomes, we see that in the successful ones we fought as hard as we could until the enemy was completely defeated. We made sure they were utterly beaten and all the fight had gone out of them. Only then did we extend the hand of friendship and try to rebuild. In contrast, our unsuccessful ventures in war have all been fought with reservation and even timidity, as if afraid that beating an enemy in battle will make them angry and will ruin any possible victory. It certainly describes Vietnam, and it looks very similar to what is happening in Iraq.
First, I think you are begging the question. You are defining success as complete and utter defeat of the so-called enemy. Unquestionably unconditional surrender was the reasonable goal against Japan and Germany. But is that always the correct goal (hint Clausewitz parts company with you here.).
A goal is not a strategy. It is mere wishful thinking. Once the goal is defined you have to define the means to achieve it, assess the cost and decide whether achieving the goal is within your means and whether it is worth the cost, and the real cost is always some large multiplier on what you think the cost is going to be because the other side always figures out how to adapt to your strategy and raise your ultimate costs.
In this regard, even if the goal in Iraq were achieveable - and I will confess a lot of ignorance as to what anyone thinks the goal really is, its cost will have been a lot higher than anyone originally estimated. A number of blunders were made including a deba'athification and disbandment of the Iraqi army in a manner that did not subtract from our ultimate difficulties, but multiplied them beyond belief.
One of our goals is clearly something along the lines of a stable democratic government in Iraq. Is that something that we ever had a chance of achieving? I don't know.
Vietnam - one of the lessons learned by the professional military about Vietnam is never ever ever go to war without a clear strategy. Our goals seemed to be something along the lines of kill all the commie b'studs, commie being defined as anyone who was opposed to French absentee landlord colonialism. Hell, we fought our own revolution to oppose just such a regime in 1776. Why did we think we could prop up the proponents of such a regime on the other side of the Pacific Ocean. We should have been fight a counterinsurgency war there, which you don't execute through Arclight operations, which just create more resentment not less.
Petraeus appears to be getting Iraq more or less right, finally. But it is after many years of other commanders doing a lot of not very helpful things that only multiplied the number of folks against us rather than reduce it.
And the first rule of counterinsurgency war is to make your friends your friends at the beginning, and no allow them to become your enemy. You do that by showing that their daily lives are a whole lot better on your side than the other side. Otherwise, they just want you gone.