I know nothing about NK's nuclear capabilities, but I doubt a few well-place JDAMS would do the job. Bombing nuclear facilities is not trivial. Israel did it successfully once, though.

A pre-emptive attack on NK could be a great idea, or it could be a disaster. There are thousands of U.S. soldiers in South Korea. An attack on NK would give them the motive they want to attack SK. I don't know if you've read about NK's elite troops. Those guys are savages... cold-blooded killers... they would eat U.S. Army babies for lunch if the combat took place on the ground.