I don't think what you say is true for serious terrorists. If they were that naive, they would be easy targets.
It seems more likely that the NSA isn't just hunting hardcore terrorist cells. Terrorists don't act in a vacuum. They are the extreme end of political/religious movements, so if they keep tabs on the radical movements from which terrorists eventually emerge, that could help narrow down the circle of those who are then tracked in a much more intensive and expensive way.
It seems more likely that the NSA isn't just hunting hardcore terrorist cells. Terrorists don't act in a vacuum. They are the extreme end of political/religious movements, so if they keep tabs on the radical movements from which terrorists eventually emerge, that could help narrow down the circle of those who are then tracked in a much more intensive and expensive way.