Everyone gave really great suggestions , def check out Motown museum.
If you are in town on a Saturday check out the Eastern Market, and stop by Russell st deli .,http://www.russellstreetdeli.com/
there may be a line , but it's worth it, if not go next door and check out Supino, http://www.supinopizza.com/
Check out sound board at motorcity casino http://www.motorcitycasino.com/SoundBoard.aspx
If you plan it right there are plenty things to do . I would rent a car . have a safe and great trip !