NK is a really tricky one. The problem with the sanctions is who gets hit hardest? The innocent, ordinary citizen.
Is diplomacy really out of the question? It seems to have worked well for Iran, although they are not the nutters they have been portrayed as (one of the most misrepresented...
The whole thing could be an intelligent ploy by NK to prevent themselves being invaded like many other non-Western countries have been. Show of some nuclear capability and demonstrate it would be chaos if the West invades. They may view the risk of invasion and regime change becomes less likely...