When the story's done, polish it with blend and flow, maybe plump it up or thin it down but don't be coerced into rewriting it. If an agent doesn't like it and a publisher doesn't like it, they're the wrong people for you. Say goodbye to them, not to the book. Usually, rewriting doesn't improve the book and withers the author's confidence. Rewrites that do work are ones which take the author in a big circle back to square one with the novel rewritten to its original version.
New writers founder on Rewrite Rocks.
Don't do it unless you're a masochist. If you are a masochist, rewrite is the place for you. It's fine to polish your manuscript but don't rewrite it, don't dismember it. Your first vision was the clearest. Do a breezy read-through and change all bad prepositions and articles that don't read as smoothly as water flows in a brook.