I don't fix rejects... I move on with my life.
While its worth looking over rejection reasons, I don't think its worth obsessing over them - basically the effort involved with trying to re-work an image isn't worth the trouble. The danger with microstock is that it can be damaging to your self esteem if you focus on the rejections.
I think its worth getting your workflow to a point where you shouldn't be getting technical rejections (eg. trademarks, noise, artifacts) but if the rejections you're getting are "not suitable for stock" then sometimes it comes down to a difference of opinion that re-submitting just won't fix. Shooting something else is usually a much better option.