Richard,
If you go back via I-75 stop over in Atlanta and stay at Stone Mtn. Campground, drive toad into Atlanta and visit Aquarium, CocaCola, CNN (all within walking distant), Fernbank museum is also close by the Aquarium area and worth a couple of hours.
From Atlanta head through Knoxville and go to Lexington, KY and stay at the Kentucky Horse Park Campground. Drive over to Keenland Racetrack and wander around for a couple of hours, might even get to see some auctions. Also, make a visit to Rupp Arena and look for the "rocking chair".
From Lexington head westerly to Louisville and then north to Indianapolis, Kalamazoo, South Bend and home.
Plenty to do an see in KY. Google the "bourbon trail" in Ky and see if you might like a nice day trip.
Edit: misread SE Michigan and I was thinking SW Michigan. We visit friends in Watervliet. Guess you could skip the Louisville to Indianapolis route.