Mike, unlike you I only have one or two photos to touch up at a time, but I have found doing it by hand (usually cloning a nearby bit of the picture in) takes less time in the long run. Yes it is tiring so best not to try and do too much at a time, and save at every stage..
Last job was to remove my wife's ex-husband from a photo of her - strangely enough (!) there isn't any software for doing this automatically, although there should be !