I detest having to defend the NSA here. I mean, the internal newsletters and other stuff may be an interesting curiosity, but unless they are documenting government crimes or violations or rights, I'm not even sure its right to release them. The NSA does actually an authorized function besides spying on Americans, and that function does require some degree of operational security.
The fact that the NSA provided assistance to interrogations at GITMO is not surprising at all and would be expected. After all, if the CIA is interrogating suspects, the NSA obviously wants to know about phone numbers, methods of communication they're using, passwords, so they can target their SIGINT, so they're going to be providing the CIA/FBI with a list of questions they would want answers to.
On the scale of damaging information, most of the damage has already been done, and I don't think these newsletters really hurt NSA operations. But one wonders, what else does Greenwald have that could be really damaging, and when they run out of other things to release, will they risk releasing stuff that has nothing to do with the abuses that lead Snowden to take action.
Most of these will just be for historical perspective soon. It's not like there is going to be any punishment for the participants of the potential wrong-doing. So it's always just served as a journalistic window into the operations and not serving some higher legal matter.