I only skimmed the other answers, and saw some of similar thought. I think that while retouching can be an art in and of itself, it is more often than not part of the larger work of either portraits or photo-manipulation and see no need for it to be in it's own category.
From my perspective, retouching falls into a bit of an odd middle ground. Sometimes I have no problems putting retouched images into photography - and I think most people don't have a problem with it, if they're being honest. When retouching gets to the point of taking off pounds, reshaping the face, adding/removing make-up, etc., it becomes more questionable as far as photography, certainly doesn't meet what most people think of as photomanipulation, but also is significant enough not to just call scraps/miscellaneous. I think a retouching area of some sort is a good idea, particularly if it's set up so that the original image is also around.
Well I think it's kind of a photomanipulation, sure not a composed one like we do, but it's still is in the first definition of the word. Maybe the photomanipulation gallery could have some sort of sub gallery for retouching?
I have no idea. I don't like to see retouched photos in photomanipulation category, so I would submit retouched photos to photography or to digital mixed media, depending on the amount of retouching done.
I totally agree with your opinion. If you retouch a stock photo, it shouldn't go into the Photomanipulation gallery, because dA considers manips to be a combination of at least two photographic elements. But submitting to Photography usually makes people think that you took the photo, even if you write in the description that you didn't (personal experience tells me that many people just don't read descriptions...) so a gallery for retouching/postprocessing would be great!