This will be an intel coup for China and Russia.
NK does their test launch, we respond as though it was a hostile launch and use AEGIS, SM, COBRA JUDY, Patriot, and lots of other goodies. We shoot down the missile. B2 and F22 fly around.
China and Russia get all of our radar signatures and frequencies, a look at CONOPS, an assessment of capabilities, plus pictures of our hardware in use and track data. Plus lots of unencrypted radio chatter, facebook pictures from cell phones, and twitter postings (Guess what I did today?)
Obama looks like a hero, and NK promises to retaliate.
I think you have the reason for this. It would be low-cost for NK, have high benefits for China and Russia, who probably have signals intelligence units parked up and down the NK beaches.