Caution, this comment contains conspiracy theory and a bit cynism.
Also apologies for delayed comment. It was intended to be posted next to this comment. So, my apologies, if it is outdated by now.
I am not a "beliver", but I there are surprisingly few contradictions. Well, I know, that's what makes for a good conspiracy theory.
There is no such thing as an ex-marine, marines told me. After someone got a marine, he will stay it for the rest of his life. Why should there be such a thing as a former intelligence agent/director/whatever? Aside: Being a former something makes a good cover story for selling almost everything to the media since the person is perceived both trustworthy and independend.
What if Snowden still works for NSA, playing the role of his life? I would really like to know, what Russians have shown or told him so far. He is smart, he learns from questions and he knows how to communicate securely.
The published documents are very well selected not to endanger ongoing missions (compared to e.g. some of the revelations made by Der Spiegel or Norddeutscher Rundfunk, Westdeutscher Rundfunk and Sueddeutsche Zeitung which endanger ongoing BND missions).
Raise your finger if you honestly belive that Journalists or German politicians (who are part of German Intelligence Control and since can be assumed under surveillance) can meet with Edward Snowden multiple times in hotel rooms without the whole five eyes noticing. If the right person gives the command, Snowden will be dead ten hours later -- or less. Resist the urge to compare to Osama bin Laden -- he was not giving interviews to tracable people.
If this would be a plot, what are the stakes?
Of course the NSA lost much of its credebility in this mission -- wait a second. Not the NSA lost credebility, the U.S. Administration (remember, the one starting with "change" and "close down Guantanamo") lost credbility. How convenient for some intelligences. The NSA itself does not even need to care about what people think about it. Or what policitians think. They got a license to lie to everyone, including those ought to control them. It literally does not matter to their work, what anybody thinks. Whoever wants to work for them will apply anyhow. Whoever needs to be working for them will be forced to do so anyhow.
Granted, some NSA programs got public. Some companies lost reputation. Still no real damage to the NSA since many of these companies are to big to fail. There is no way to evade Microsoft's products if you're running a multinational business. Tough many people are aware of this, the big jump to FOSS in corporate environments hasn't come yet. If I were NSA, I would bet it will never come.
Hint: Has there been any statement of the NSA stopping any of these programs (aside from the Merkel thing)? Has there been any real damage to the outcome of these programs?
What could be motivation?
Once programs are leaked, new programs need to be funded to replace them. Big programs. Expensive, powerful programs.
Edited to Add:
Regarding theories, we have a medival problem. We cannot prove if it's the sun turning around earth or vice versa. We just have observations. Many theories are out there to explain them with few or no contradictions. This makes none of them truth. We just have to realize and perhaps also accept that we cannot decide without further knowledge.
We can - however - use these theories: Act regarding to the worst-case consequences. Encrypt. Be subtle. Stay within the crowd. Don't expose. Avoid being diagnosed with paranoia.