Sorry, you're not going to have much luck. Outside of the parks, there's just not much challenging that's legal. I agree with you that it's far more fun to be out in the wilderness than surrounded by other people on a couple acres.
However, as mentioned, snow can turn otherwise boring seasonal roads into interesting trails. I recommend checking out any of the state and national forrests when there's snow. I assume you've been to Manistee? But it's not fun
to get stuck on a snowy trail with nobody to pull you out so make sure your Jeep can handle the amount of snow. You should also be mindful of snowmobiles.
In the below thread, a user mentions good wheeling between Traverse City and Kalkaska. I checked out this area last weekend. There's potential, but I was limited by the amount of snow so I could not fully explore.
The UP is also more interesting than the LP. The Keweenaw has some nice trails and there are some in Hiawatha National Forrest. I went up that way in late fall and would recommend it to anyone. There was just enough snow on the ground to make it interesting, and there was nobody else around.
Drummond Island is supposedly good. I've never been so it's on my list this year.
Go to the Michigan DNR website for a list of all ORV trails. It will tell you which trails re open to Jeeps, and you can print all of the maps. Aside from seasonal roads, this is what you're limited to.