The leaking of the Snowden wires was a sad day for America, I think that we as a country have known for a long time that some of the things that are done to protect our freedom, some people might find objectionable, the man broke the trust of our country an put American lives on the line.
I think it makes the US government look bad. I would try to keep secret things under wraps. Government secrets about national security or matters like it should be known by as little people as possible. The government has to only show it's good side and keep embarrassments to a minimum.
I believe the US itself is harmed more by the US Embassy Cables leaks. Given that these events happen through the Embassies is a problem for the United States, but it is also our government that is losing information and having classified information spread throughout the community, both abroad and at home.
I think that the primary entity harmed by the cables leaks has been the United States itself. Those leaks showed some private bits that should have stayed private. It was sort of like being sent a screenshot of your Facebook friends bashing you. Embarassing, awkward and not at all helping one's credibility.
These Embassy's are the United States. Any information leaks from these Embassy's will harm mainly the United Sates. It does harm the other countries in which they are in, but most of the documented information would be of the United States, or of relations the United States has of this country.