Nuking N Korea would be an instantaneous, cost effect solution. It wouldn't cost us a thing, save the very same excess nuclear inventory we're trying to figure out how to retire anyway. Our older, dirtier warheads would do the job AND retire themselves in one shot.
There would be some public grumbling, but most of the world would be quietly glad we removed this thorn from everyone's side.
Finally, such a strike would represent an unprecedented and effective real world test and display of our nuclear capability. I'd wager that Russia, China, Iran, and others would pay more careful attention to our needs afterwards.
After the place cooled down a bit, the Chinese would take advantage of the extra lebensraum and set up a few toy factories. They'd secretly be happy, too.