Basically, the US has no good options. The six-party talks will not result in denuclearization, not any time soon at least. Ignoring North Korea
raises the prospect that North Korea will up the ante in its bid for attention.
Boxing in the regime through tougher sanctions only feeds anti-N Korea sentiments in Japan and the US, not to mention risking regime collapse altogether. Plus it just gives the North one more button they can push to get attention and create issues for which the West convinces itself it must negotiate. There is no good option available to the US, Japan, and South Korea, especially in the absence of more Chinese pressure.
And the North is without question making progress with its missile technology. While the satellite launch may have failed, this rocket still flew more than twice the distance of previous long-range missile tests. So China should be worried. Any move to develop longer-range missiles, particularly rockets that could reach their mainland, could spark a new arms race in the region. And there have been calls already in both Japan and South Korea for those countries to begin developing a pre-emptive strike capability. At the very least US and the neighbors in particular should be devoting considerable energy preparing for the consequences of a possible NK regime collapse.
The only course of action at this point may be getting a token a resolution out of the Security Council and doing whatever possible to coax North Korea open while waiting for 6 party talks to resume. China and Russia have more leverage as a result of their trade relationship with the country, but tightening sanctions doesn't seem to be the way to go either since those have only made the suffering of the people greater. In any case, the top priority of the Chinese seem to be to preserve the North Korean state as a buffer between it and the U.S. sphere of influence. China clearly wants reform from North Korea, just not at the expense of it as a viable state.
So the ball in now firmly in the court of the DPRK. Let them know we're interested in restarting negotiations over the nuclear issues, give them plenty of incentives to cooperate and then spend as little time as possible on this subject before dropping it.

We have a lot more important things to worry about than calling the North Korea's bluffs over a puny bomb. Once and for all, it's time to stop playing their game.
