Duncan,
The work you're doing in Detroit sounds very interesting. Having grown up in the area, I'd be interested to hear more.
Detroit Golf Club is definitely worth a visit. It's a neat, historic club, in what has become a somewhat bizarre location in the heart of the city. Great clubhouse, too. As Mark says, the clubhouses at Franklin Hills and CC of Detroit are must-sees as well. And, Franklin Hills is an exceptional Donald Ross-designed course... not far from Oakland Hills.
My home club (Essex G&CC), across the river in Windsor, Ontario, features a neat, old clubhouse that was built along with a solid Ross-designed course in 1929, too.
Plum Hollow is probably the most under-rated course in the area. It's a really good golf course, designed by Hugh Alison, located just off the now infamous 8 Mile Road... back when Colt and Alison kept an office in the Penobscot Building, in Detroit.