Should I retake my A minus class in my last semester?
TL;DR: Probably not worth it. Take something else and expand your horizons.

From a knowledge perspective, you're not getting anything out of this. You got an A- in the course -- on a transcript, that should tell any graduate school that you understand the material in the course.

So any potential gain here would be for your GPA. On a 4.0 scale, an A- is a 3.7. If that 0.3 is the difference between a 3.5 GPA and a 3.4 GPA, go for it. Otherwise, find yourself another class and accept that you aren't perfect (nor will any graduate school expect you to be).