Yeah, ironically, the US's approach to state secrets (as in fucking everything is a state secret) makes it harder for them to keep things under control.

But in that case, a leak only has a 5% chance of being something that anyone actually cares about. ("Anyone" here does not mean the overly paranoid bureaucrat that classified it, it means pretty much anyone else.)

Not necessarily. The other 95% (as evidenced by Manning's leaks) often contain information of importance to commercial enterprise -- information that should likely be of public record anyway if it's being communicated through publicly funded channels.