If you are of a suspicious and partially paranoid mind like me, you might think that the whole thing was a scam to set up the Bush admin. They could always claim that no one could investigate Wilson's wife for national security purposes. The Bush admin would be between a rock and a hard place. With liberal Big Media cheering them on, the special prosecutor would go after the evil, war-mongering Republicans with claws bared. The CIA anti-Bushies and the Wilsons could sit back smug and satisfied, laughing at all the harm they could do. And actually their plan is working quite well. Wilson is the perfect actor and media whore for this operation. You're right, under normal sane circumstances he should never have been considered for anything except drinking mint tea at diplomatic receptions. But if you're overly suspicious like me, his appointment makes sense.
That makes two of us.