It is something to pay attention to and be concerned about. They are nuts, are trying to show toughness and gain respect, and.....they have nukes.
I would be more worried about them causing havoc in east Asia and putting a huge dent into the global economy.
A read an interesting thesis the other day how north Korea could win a war against the south. The cliff notes version would be to use nukes as a tactical first strike with an upper atmosphere blast over south Korea creating an emp blast and leveling the military playing field where they would not be at a technologic disadvantage. Then immediately after the emp launch massive amounts of forces south to take advantage of the chaos. They could in theory take 10,000-100,000 US citizens hostage as human shields that currently live in south Korea before we decide how to counter attack.
It was an interesting strategy.