The Indian mounds in Macon are interesting and any Georgia state park is worth visiting for a few hours, there are several close to your planned route. However none of these are must-visits, they are nice places to spend a few hours. Have you considered spending a couple of days on one of the islands near Savannah? Hilton Head, Jekyl Island, St Simons Island and Amelia Island are all pleasant places for a beach stay. Amelia is probably the nicest but a couple of hours off your intended track.