I always see things in a piece of artwork that need to be corrected, adjusted, fixed AFTER I scan or photograph it. Not sure why that is, but I think it has something to do with the distance between me and the piece. When I'm painting on something, I can totally miss/not see an area that screams to be worked on (yes, we've already had this conversation), but it is also a very useful tool for those times when you're stuck and you don't know why.
Scan or photograph the artwork, take it into an editing program, like Photoshop, and if you can, make it a grey scale. That almost always shows me areas that need to be adjusted. It also adds that distance - instantly - so that you don't get surprised when you see it hanging on the wall in a show and think "Oh good grief, did I really not see that?!!"