I agree with your remarks generally about the proper advice from a lawyer to a client--if he has something to hide. Although in this political climate, taking the Fifth would be political suicide because it would be looked at as an admission of guilt by the masses, egged on by the MSM.
However, how do you take the fifth on a question that is never asked?
I don't think the matter arose until Judith Miller testified and probably dropped an aside that she'd had some previous conversation with Libby in June. That's why she went back and produced notes from that time and now has been called back to answer questions about them.
Of course, we don't know what was the subject nor the substance of the June interview, but it could hardly have been Wilson/Pflame because Wilson hadn't come out against the administration to that point. Unless Miller revealed that Wilson was in negotiation to publish something with her paper on the subject of his trip.
Lots that we don't know here.
It might help you if you knew the social milieu that Wilson and Plame live in. They're social butterflies who actually live in Washington DC in the same social circle that includes the Kerrys and various reporters for the Washington Post and the New York Times.
And Wilson has a very big mouth.