Pictured rocks is about at the edge of your drive time limit, but offers great hiking and views. You'll be getting beautiful colors up there in early October (I'm heading up there around the same time). Tahquamenon Falls in Hiawatha Natl Forest is beautiful as well - great colors, nice day hikes, beautiful waterfalls a bit closer than Pictured Rocks. Tahquamenon is a great spot for winter camping as well. North Manitou Island would be another good choice - after Labor Day it doesn't get much traffic. The ferry out to the island only runs on Fridays and Sundays through Oct 11, and is unavailable after that, although you may be able to hire a ride out there through the local marina (I've done that in the past, and saved travel time as well. You just have to have faith that they will pick you up after your hiking!) Sleeping Bear dunes region is another good area.
There are plenty of good day hiking locales as well in the lower peninsula, but it depends on your tolerance for seeing other people during your time. I've also heard good things about the Bruce Peninsula in Ontario, but have never camped/hiked there personally. It is a beautiful area though.
Another option would be to head south. You're about 5 hours from Red River Gorge in KY, and that has lots of good trails, nice colors, and backcountry camping, so avoiding setting up your tent next to others is pretty easy, especially during the week. You might be a little early as far as colors go - I'd check with someone in that region for more info (you can call them at Miguel's Pizza - google it, and they'll fill you in on conditions).
Hope this helps!