My memory from an American Foreign Policy class I took back in the day is that the NSC advises the president on issues of national security and foreign policy, and then acts to coordinate responses through the various involved agencies. Where I'm hanging up on this in my mind is that, to me at least, intelligence would seem essential (as would knowledge of military assets and capabilities as well) to discussions of national security and foreign policy issues. If you want to expand the council to include an adviser, knock yourself out, Mr. President. But why are we having some pretty important assets/advisers seated at the kiddie table instead of with the grown ups trying to make decisions?