CG Highlands

So, i'm watching this chap wi his d?SLR camera, taking shots of the hill. I think that i could do something with that view. Intensify the clouds, turn it into a really dramatic photo, instead of the Force 6 westerly coming in from the, err, west. But the view doesn't exist in real life. It would be a construct. So why not just build the scene from some computer elements? At what point does modifying the shot taken become an exercise it the creative manipulation of the image? Should photographers list their manipulations as a matter of course? I think of these things when it is cold, heats up the brain.