No, the worst possible thing already happened, thats the content of the letter.
A slight exaggeration perhaps, but it's beside the point. It's not a competition of who can be more wrong; the fact of the matter is that it's possible for two parties to be in the wrong. And in principle, how wrong one party is should not affect how wrong the other party is.
Think about all those legal penalties for spying, warrantless searches, torture, and all those other illegal methods for obtaining potentially valuable information. Not only do we punish people who use them, we refuse to acknowledge, in court, the information obtained using them. Why? Because if we did, then people would continue to do them, regardless of the penalties. It's not enough to say, "Whoops, my bad, but at least you caught the serial kiddie-fiddler due to my illegal search!", and walk out scot-free. Regardless of how useful the information exposed, we know that the methods to obtain said information are evil, and we do our best to ensure they don't happen, even if it means ignoring valuable information. Basically, as far as the courts' are concerned, the ends never justify the means.
(Now, I don't mean to suggest we should ignore what Snowden turned up, just that we shouldn't allow the magnitude of NSA's crimes to blind us to the issue of whether Snowden himself has done wrong or not.)