The spies whine and spin it their way. If what they were doing was so innocuous, uncontroversial and even beneficial then they would be happy to be praised in the press. The fact is what they ware doing is deeply offensive to a large segment of society and they wish to hide it.
As to whether the terrs benefit or not, only the stupid ones might and they probably aren't reading. The non-stupid terrs have known about surveillence since before Echelon and adjust accordingly. They won't even infer any limits because they know the release is vetted to be incomplete.
The real effect of Snowdens releases is to confirm the tinfoil-behatted. Many fringe people have been saying much the same thing for 10+ years and been dismissed as lunatic paranoids. Now it appears they were right. Many people have egg on the face (congentially oblivious).