How many times do you come across a mix that nothing you do really improves it? What you do may change it and it may sound fine that way, but it really isn't any better than the original.
That happened to me today. Maybe it was just the nature of the material. Maybe better gear would do the trick. Or maybe I just couldn't hear what it needed - I don't know. But whatever I tried just didn't warrant changing it. Its not a high profile project by any means so it won't be the end of the world if its not "perfect" but it just has something by itself that gets taken away by processing it.
So I just left it alone...