Belvedere is a perfect stop for a GCA group. It did indeed rate a Doak 5, which I agree is about right. It would merit a higher rank on "charm" factors and perhaps a lower rank on some "challenge" factors. The constantly repeated story is that Tom Watson's family regularly summered away from the Kansas City heat at a cottage in the Charlevoix area, and Tom played Belvedere often, and calls it one of his favorites. The story is no doubt true, but probably a little threadbare too. I am glad that someone in the Doak firm is looking after it.
For many years, the Michigan Amateur was contested over two courses in northwest Michigan. Medal play qualifying was held at Antrim Dells (south of Belvedere), with match play conducted at Belvedere. And that, I thought, was a very good way to conduct the competition. (Other formats and locations have been utilized in subsequent years; with the wealth of choices of northern Michigan resort courses, there were other course options with more convenient and modern accomodations and accoutrements.) I think that GCA visitors will be very admiring of the test that Belvedere can provide as a match play course. "A fine little course" is how Mr. Doak described it.
(By the way, if you have the time, there is no reason to avoid Antrim Dells. Tom Doak accurately described it as "A well-liked public course... with a few good holes..." with some "sameness" to perhaps too many of them with flanking bunkers. A Doak 4. Antrim Dells' back nine winds through some spectacular woods and is a dleightful tour if not an inspiring golf course architecture tutorial.)
Dunmaglas is another course nearby to Belvedere that is worth seeing if you have the time. Also a Doak 5, it merited some discussion in The Confidential Guide.