Good list, CGSwans! I have a few reactions, but nothing serious. I'd recommend Milwaukee or Toledo, instead of Detroit. I would try to squeeze in the Tennessee Aquarium (possibly a Top 5 aquarium) onto the same trip with Atlanta. I also think the Memphis Zoo is probably the best zoo you're leaving out. I also wouldn't go in any way out of your way to get to The Wilds. It's very limited, and simply not worth any kind of extra journey. They get about 20,000 people a year there.
Detroit - I simply must see Arctic Ring of Life one day. Amphibiville too.
Milwaukee County Zoo - I guess it's kinda on the way between Chicago and Minneapolis, isn't it?
Toledo Zoo - close to Cleveland so could go on the list without upsetting the girlfriend too much.
Tennessee Aquarium - the problem with adding more aquariums to the list is that I wonder what could match it with Georgia, Monterey Bay and Shedd? What does Tennessee have that is in the 'unique' category?
Memphis Zoo - it's on the list! Sort of poked onto the 'Deep South' tour.