In 2007 I went on a trip to Yorkshire, and took a photo of the River Wharfe, near Grassington.
It was ok, but I've not really been entirely happy with the image, and I decided to have a go at re-processing from the same digital negative. Advances in software alone can often make this a worthwhile activity, but in this case my own improved processing skills along with a more refined ability to determine what isn't right about an image also came into play.
It may not be an image that'll win any awards, but I'm satisfied with the degree of improvement I was able to make, and more importantly that I didn't simply settle for being just a bit better than before - fixing the crop and exposure took it a long way - but for each revision I looked at it and kept asking myself "Am I happy with this? How could it be improved?" and made quite a few tweaks before I could say there's nothing more to add, nothing more to take away.