Then why is the allegation about classified status in the indictment? It's to set up the materiality of the perjury, right? The defense is entitled to test that, don't you think?
I think it is necessary background to explain why the subject was the point of so much speculation between the WH and the press corps. If it was literally true that "everybody knew," then the case easily evaporates. There has to be at least a pretense in order to support the nature of the conversations.
The defense is entitled to whatever it can find and take. But note that the defence "no crime because Plame is not covert" is exactly the same defense that Miller and Cooper asserted in order to get out of testifying before the GJ.
Its purpose is to show that Libby had a motive to lie, because he thought he would be in legal jeapordy if he admitted to disclosing to a reporter Plame's theretofore not known by persons not entitled to know status, which status was classfied, and known by him to be classified.