Hmm, I hope I didn't scare everyone else away with my long post! I thought of another place you don't want to miss: Frankenmuth. The town has a Bavarian theme. Home of Bronner's Christmas Store (all year around Christmas decorations), Zehnder's Restaurant with their chicken dinners, and dozens of specialty shops and souvenir places. The Frankenmuth Brewery has a variety of good beers (from IPA to Dunkel) and good food; I recommend a pizza and a flight (several small sampler glasses of different beers). You could spend all day here.
If you go beyond the U.P., one area that stands out is the north shore of Superior in Minnesota. There's a series of nice state parks, most with waterfalls because there is a sudden drop-off in topography paralleling the shoreline. Be sure to turn off and see Palisade Head, where you can park and stroll to the edge of a cliff, with the lake straight down below you about 200 feet; if the weather is nice, you're likely to see people rappelling up and down the cliff face. There's a nice hike to a similar overlook just up the highway, in Tettegouche SP. You'll need reservations to camp in a state park here, they're popular, but without reservations you should be able to get into one of the NF CGs, like Eckbeck near Finland (small sites but a few are do-able). At many of these state parks you can find pleasant hikes along the riverbanks above & below the falls, and at one (Temperance or Cascade, I forget which) I saw teens jumping off the rocks into the river below, maybe 15 feet down. (Of course all the bikinis might prove hazardous and cause your boys to suffer eye strain.) At Grand Marais (yes there's one in MI and one in MN!), have a pizza at Sven & Ole's and then walk out past the coast guard station to Artist's Point. Then drive the Gunflint Highway to the NW from town, back into the wild woods where you can hear the loons; you have several NF CGs to choose from along there.
