FWIW, I lived my first 22 years in Michigan, was back for five years of school, and once or twice a year almost every year since. Several years of my youth, and my back to school years, was camping (not RVing) in the small lake recreation areas west of Detroit, and the U.P.
This year I'm paying a small fortune to join an escorted tour visiting Mackinac Island and The Henry Ford (already visited more than once), and will likely road trip back shortly afterward, for most of the summer.
My top places to visit for camping and outdoor recreation are the northwest L.P. (Charlevoix, Antrim, Grand Traverse, Benzie, Leelanau counties) and the north shore of the U.P. (Marquette and Schoolcraft counties, and the Keweenaw).
My top sites for sightseeing are Mackinac Island, The Henry Ford, the mine tours in the Keweenaw, and the Air Zoo at Kalamazoo (admittedly a special interest). My wife and daughters always thought Frankenmuth, and the Christmas ornament store, were special (it is also on my escorted tour), but I don't get the point, I've seen where all this stuff is manufactured in China.
The Soo is definitely worth a visit if you've never seen locks work. Great Lakes Shipwreck Museum if that's an interest, was for me because wrecks on the lakes were still common enough to be news when I was growing up. There's a ski jumping museum in the Marquette area (seems the sport was invented there?) if that's an interest, but a ski jumping hill in summer is just a hill.
Detroit may have deteriorated as a city since the '60s riots and flight to suburbs, but the culture (museums particularly) are still there. Lansing is another good center for studying Michigan history and culture, the state offices and archives concentrated in the capitol.
Camping and outdoor (esp water) recreation is good in southeastern Michigan, and in the forests intermixed with farmlands north of US-10. All the L.P. shoreline is dotted with lakeshore parks, but the way winds and waves work, the Lake Michigan shore is best for beaches, Holland to Manistee being popular, and north from there maintaining substantial "summer people" resort populations, since the late 19th century.
So what is it that you want to do?