That is true, the Michigan State parks, with the rare exception, do not have full hookups, and the power is rarely 50 AMPS.
We rarely stay in public parks in Michigan, and just do the no hookup thing at the State Parks.
Our state parks in the UP are quite beautiful.
I can advise against ONE park up there, which is a KOA near St. Ignace. Our experience was less than stellar at that particular park.
We did stay in a city park in Marquette that was pleasant, would stay there again.
And, if you can stay in Munising, and love to hike and waterfalls, you are in for a treat! Also Pictured Rocks there. We did stay in a public park there, but so many years ago, don't remember name or details.
Of course, do not miss the Falls, Newberry. Seems we stayed in a public park there as well, but, again, way to long ago, so I cannot remember.
Island State Park, DO IT! if only for a few days, and visit the other parks in the area.
Photo at bottom of this page, is of that campground
http://www.geocities.com/genieyorks/uptour2002.html
I did not put the rest of that tour online, if you are interested, I have a word file on it. Email me if you want the document.
Some of this is close enough to each other that you could do day trips.