We're very fortunate to have hills in Ann Arbor. I rode a mixed 30 miles yesterday.....everything from dirt roads (warren is hardpack, wicked fast, and not sloppy at all) to pavement, b2b, and sections of non local loop trail. There is no mud on my bike. The worst thing going was all the salt on the b2b. Avoid with your fancy MTB. Normal surface streets are clear though. If you have the sense to ride trails that have direct drainage and loose, open substrate, you can certainly add a splash of wild to your dirt road rides. If it's flat, or clay, stay off. If you can't tell the difference, stay off all together.
I've got to agree with Bcar and IPB on this. Keep Ann Arbor wild. Every year I live and ride here, I find out about more stuff. What started out as a three mile loop behind my apartment has turned into a 9 mile loop....without having to cross a road. I hope to have at least 20 miles of trail strung together by the time riding season is in full swing.....not including the "local loop"
We are fortunate to have lots and lots of unregulated park land, and a community committed to preserving its green spaces. We are fortunate to have trail workers who keep stuff going for the sheer love of the sport, not to ask for outpourings of gratitude. Trail workers who go well out of their way to keep a low profile.
I love riding by myself and exploring, and I love riding with people. I know bcar does too. Chances are if you ask, like I did, someone will show you around.
But you can't blame people for being coy. I'm working hard to make a career for myself in Washtenaw county, because I can't think of any other places in Michigan below the 45th paralel with this many different kinds of riding accessible without getting into a car.