Attacking Iraq will leave us open on that flank. Their odds of success still won't be good, but they'll likely never have as good a shot again. Every general in North Korea must be thinking, "If there ever was a time when this idiot plan of invading the South were to work, it would be now, while the U.S. is tied down elsewhere."
Not to say that we shouldn't attack Iraq, just that we should keep an eye on Junior while we do.
Totally agree with your assessment that Iraq II--if it gets the US bogged down--will be the only one or two chances that the North will have to launch their blitzkrieg. The other time might be a PRC attack on Taiwan. Would the US 7th fleet pull south to defend Taiwan? What about a 3-front war: 250,000 US troops somehow bogged down in Iraq, NK launches southward, PRC attacks Taiwan--at the same time? Add to that the on-going terrorist activities of al-Qaida and we have a WW III (or IV depending on whether one counts the "Cold War" as WW III).