Down and Back vs. Back and Forth
As you've currently got things planned, you're looking at 1800 miles to get down to Key West over 10-12 days, and then a Speed Run of sorts on the way back, covering 1300 miles, which will take 2½ days with only food, gas and restroom breaks. That's not a great way to end a trip. Yes, I'd suggest that you "hit some of those on the way back". It doesn't matter, except perhaps to you, whether you do the coast or the mountains down, but the coast trip would include Richmond, Charleston, Savannah, Daytona Beach, and Miami, while the mountain trip would include Jefferson National Forest, Great Smokies Mountain National Park, and maybe Atlanta and the Florida Gulf Coast. By the way, is there a reason that Charlotte is included? because if you drop it and use the two sets of way points I've just listed, your save a hundred miles or so of driving, but more importantly, you can make the trip a bit better paced spending roughly the same amount of time going down and coming back.
AZBuck