Personally, all I do before uploading images to Commons is the occassional rotation, crop or slight sharpen. However, I've been uploading too many images to have time for much else.
As for WLM, I don't recall any mention in the judging criteria of the desirability (or otherwise) of various post-processing techniques. If I was looking to select an image for a Wikipedia article, I would be reluctant to choose a heavily-stylized image. Of course, WLM and Commons are not looking to merely provide an image bank for Wikipedia.
Perhaps the judges could consider providing some guidance about HDR and other post-processing techniques for next year's WLM ?