I'll look for Burt at the gathering.
I can think of several good places you guys could meet on the water. Along with Lake of the Ozarks, there is the Mississippi River. Anywhere between Minneapolis and just north of St. Louis. The Alton marina north of St. Louis is a great spot to launch out of. There are several free parks/launches on the River in Dubuque also. Some great lakes in Kentucky would include Lake Cumberland. Very pretty area with a lot of lake to explore. I'd recommend using the Jamestown Safe Harbor Marina to launch and for parking. Then there is Lake Barkley and Kentucky Lake with Land Between the Lakes Recreation area between them. Lake Barkley has the Cumberland River, and Kentucky Lake has the Tennessee River, both great cruising opportunities. I've used the Kentucky Lake Dam State Resort Park for parking and launching. There is also Dale Hollow Lake, however I haven't been there in a while. All these places have numerous marinas or great anchorage spots. Greers Ferry Lake in Fairfield Bay, Arkansas is a nice area also. Lake isn't all that big, but offers nice boating. There is a nice Wyndham Time Share resort in Fairfield Bay on that lake. (Thus, with the sister in law's points, we've stayed there a few times.

) Table Rock Lake is a large lake near Branson, Mo, which has a lot of good shows. I'm a lousy fisherman most the time, but all these lakes are known for good fishing.
Then on a larger scale, you have the Great Lakes. Lake Michigan has Door County, which is the peninsula between Green Bay (body of water) and the main Lake. Lake Superior has the Apostle Islands, and Isle Royale. You're on big water here and storms can keep you holed up in protected Bays. Basically like your ocean, but without tides and currents or salt. And our waves are short spaced, more of a confused 3-4' chop at times.
You could spend an entire summer here roaming around on the various waters. But if you are looking to spend a couple weeks cruising, the Mississippi, Cumberland and Tennessee Rivers all provide great opportunity to do that. The Mississippi of course is the most challenging with it's wing dams and commercial tow traffic. The Tennessee and Cumberland rivers have barge traffic, but not as busy. And no worry about wing dams. Lakes Barkley, Kentucky, Cumberland and of the Ozarks all offer a lot of water to spend time on, with numerous marinas or locations to anchor. All the rivers would require going through Locks, but really not all that challenging. If you don't want to do locks, then stick with the Lakes. I think you'd enjoy any of these places, and they'd all offer some great scenery. Most the Fall Colors on these bodies of water won't materialize until October. Except for Lake Superior. Then you might see some color in late September. And the recreational traffic really slows down once school starts, not to mention you can start seeing some frosty nights.