Maybe it's just me but the bluster coming from North Korea seems "different" this time around. In the past the gambit has been to push back inspectors when they got too close or to extort another round of humanitarian aid. I don't think those theories apply this time, at least not to the same degree.
Near as we can tell there is no internal opposition to Kim's reign so distracting interanl enemies with an external fight doesn't pan out.
I think Kim perceives Obama as fundamentally weak (and I'm sad to say I agree with him) and perhaps a strong demonstration will cow the US into more aid with less meddling. Now, I'm sure Kim is well aware of the financial "troubles" the US is currently experiencing but to him we're still slopping over with wealth and by Mao he wants some. The fact that Obama would be cutting his own political head off if he gives Kim money after quadrupling national deficits in his first 3 months seems irrelevant to Kim.
A second nuke test and numerous missile firings in several days is one helluva display. Now Kim has declared the armistice rescinded. It's easy to wave this off with, "We've seen this all before" but the numerous missile firings and another nuke are damned expensive, especially to a nation such as North Korea. That money has to be gained back somehow. Either we give it to him or he's gonna start selling parts to Iran or anyone else. We can intercept the shipments but Kim has stated that is an act of war.
Yes, more bluster, but is it mere bluster?
It's hard to imagine a mugger firing a warning shot--let alone several warning shots on a very limited supply of bullets--only to passively stand idle as his intended mark walks away. We talk much about "credible deterrence" in regards to our own foreign policy objectives (well, we used to anyway), it seems foolish not to consider the North Koreans aren't just as cognizant of these considerations.
What does Kim want and just how far will Kim go to get what he wants?