https://en.wikipedia.org/wiki/July_12,_2007_Baghdad_airstrik...
I am not aware of any major wrongdoing uncovered by the diplomatic cables leak. The comments I read/heard from diplomats who reviewed the data rather implied that the US diplomatic staff is doing its job rather well, with often an accurate description of the internals politics of the countries they cover. Leaking these memos certainly resulted in a few red faces as private, undiplomatic comments made it to the front page. But I don't see the benefit.
That leak is more akin to the sort of reckless leaks where massive amounts of private, sensitive data made available by unscrupulous hackers just because they could. This is a very different animal from the Snowden leaks which did uncover major wrongdoings and were filtered responsively.
I don't know if you would classify this as merely 'somewhat interesting' confidential information, but personally I am glad it was released and I think the public has a right to know about these things.