While ultimately, the last word is yours, I wouldn't recommend using rendering time to redo both first chapters unless you're sure to be satisfied with the result. Then, it depends on a lot of things. Do you just want to upgrade the render's quality? Do you intend to change the scene's composition? Do you have a quick way to just launch a batch while you're doing something else (writing script, for example)?
I'm sure you know what you're doing, but to me, those two chapters are far from ugly, so I wouldn't fret so much in your shoes. But as I said, ultimately, the choice is yours. Ours is to support you.