It's worth strolling around downtown as well, although non-sanctioned street art is militantly monitored and prosecuted. Even Shepard Fairey, in town to paint a giant mural on a downtown building, was charged with a felony for a bit of freelance work he (cough-cough) allegedly did in the area (some of which is still available). You'll also want to stop in at The Z Lot, a muraled parking garage, and, in the alley next door, is The Belt, sporting a great collection of sanctioned street art by Hush, Vhils, Fairey, Tristan Eaton, Faile, and others.
And then, just randomly wandering about town (I accidentally found a Swoon on the north side of Detroit while investigating the transition from urban blight to suburban might) you can see wonderful work.
Well worth the visit!
(I waited 40 minutes for a 10-second gap to catch that mural without a large truck parked in front of it!)