I have retaken one pre-req after taking the MCAT (so then its like taking it three times 1. original attempt 2. went over the same material while studying for the MCAT 3. the retake) like you are thinking about.
And you are right, it was very boring and hard to get through. And I felt useless in there because I was taking the same course for basically the third time.
But, if it that course is done soon (middle of August or so), I might do it if I were you.
Also, are you sure replacing a C with an A raises your sGPA by that much? That seems like a lot.