It is oversimplistic to say that papers add nothing of value. Surely you admit that the NYT, Wash. Post, and WSJ do original investigative research? Others papers sometimes do this also, although this seems to be decreasing. Everytime I visit my hometown in flyover country, I am frightened by how worthless the local paper has become. But there was a time, not long ago, when that paper had a staff in most major cities around the world. I assume that we are simply missing stories that would otherwise have gotten broken with more feet on the ground. (We don't realize we're missing them since we are missing them...)
Maybe the economist et al. are adding staff, but I suspect there are simply many fewer total investigative journalists, and so less investigative journalism. Maybe if the Chicago tribune hadn't cut so much, they would have broken the Blagojevich story instead of the FBI?