Porcupine Mountains: be sure to spend time at both the east and west units. The W side has more rustic camping (and is likely to be less crowded), and has 3 waterfalls in a row on the river there. You can walk along the river for over a mile each way (even cross over on a bridge and hike the other bank if you like) and it's very pleasant. The E unit, of course, has the high overlook with Lake of the Clouds. An alternate campround I've enjoyed is the Ontonagon municipal CG, right on Lake Superior with sandy beach.
Bond Falls near Paulding is IMO one of the best waterfalls in the state., maybe even the best. I actually think it's prettier than Tahquamenon.
The Pictured Rocks boat tour is pricey but I always say it's worth it, because you are getting entertained by the captain's humor as well as enjoying the scenery. You do want a sunny day, and the late afternoon 'sunset cruise' provides the best light
on the rock cliffs. Weather along that shoreline can be iffy; you can hit a day of overcast, or rain, or even heavy fog. Hopefully if you get there on an off day weather-wise, you can stick around a day or so and hopefully hit a sunny stretch.
Definitely try to leave a day for the Keweenaw Peninsula. McLain SP is nice and is also right on the lake (but it's popular, so either have reservations or an alternate CG in mind). The drive on M-26 from Eagle River to Copper Harbor is a scenic treat. Maybe take a picnic lunch and stop at one of the parks. Ft. Wilkins SP also has nice campsites (a good alternate) as well as historic fort buildings.
If you want a place between Munising and Tahquamenon, Woodland Park municipal CG in Grand Marais is nice enough and is right on the water. Just W of town there's a neat sand dune that you can climb for a view.
North of Tahquamenon, you might like to drive to Paradise and see the tiny lighthouse-turned-museum there.
When you cross the Mackinaw Bridge, be sure to stop in Mackinaw City for an hour or so and stretch your legs. Browse through the tourist-trap shops, see them making fudge and caramel corn. At the E end of the strip, by the dock entrance, walk north a half block to the local bakery for some of the best homestyle cinnamon bread or pecan rolls in the region. Mackinaw City also has a fort and a lighthouse right in town (plus another lighthouse about 3 miles west, and another one at Wilderness SP some 8-9 miles west of town).
For a CG in between there and Delaware OH, my choice would be Sleepy Hollow SP north of Lansing... but that might be a bit out of your way. If you prefer to stay on I-75 to US-23, then there are several state parks downstate but I haven't been to any of them. Hartwick Pines SP near Grayling is nice, and a stroll through the big trees in the virgin pine forest would be nice, but that could make your next day overly long.
I grew up in Michigan... can you tell?
We go back every summer for a visit, too.