Things I would do on a return trip...
-Allow more time for Wisconsin's portion of the Great River Road.  There are a lot of things to see within 30 minutes of the road. 
-Different times of the year, will allow you to experience different things in the northern section of The Great River Road.  Plan accordingly for what you want to see.  Fall colors driving the road are beautiful! 
-Schedule a fishing guide while in Bemidji, MN.  They have great fishing there!  
-There is a lot of empty space between the Minneapolis and Bemidji, plan accordingly.