When I'm staisfied I can't possibly cram any more details into the image and still like myself, I make a merged copy of the whole image to a new layer (Shift+Ctrl+C, Ctrl+V). On this merged copy I try out some level adjustments to give it more oomph. In some cases some color adjustment (with for example selective color) on the merged copy might help the pic as well.Before:After:And that's it.