From what I've read, America's enemies already knew the satellite exists. Even amateur satellite trackers knew about it, had been tracking it, and had projected its capabilities. They just hadn't actually seen the results before; because, the results hadn't previously been in an open source. Any strategic loss due to dissemination would seem to be slight.
Keep in mind; also, that enemies are not the only reason for classifying information. Some things are classified because they're deemed unsuitable for American public consumption (e.g. One can imagine how this information could play into conspiracy theories about the US government spying on American citizens; or, tracking illegal aliens.)
Sometimes it's just a political call that depends on the political climate at the time of classification and again at declassification.
A little about what others already knew,
here.