I think it's up to you, if you want a change of scenery at your campsite. From Grand Marais to Gooseberry Falls is only about 70 miles, a comfortable day trip. From that point to Duluth I don't think there are many sights to see, unless you want to visit some places in Duluth itself (such as Glensheen).
Enjoy the state parks, with trails running along the riverbanks and views of waterfalls. Be sure to stop at Palisade Head, close to Tettegouche SP, for a splendid view of the lake far below. Enjoy a stroll out to Artist's Point at Grand Marais, and grab a pizza at Sven and Ole's.