I haven't been to Valleyfair, sadly, but I have been to some of these places!
I took a trip to Minneapolis one October for an honor society thing in college. It was really cool, it's fun to walk around outside downtown, and if it's raining or something you can pretty much get anywhere without going outside because all the buildings are connected by these cool hamster-tube like things. The whole downtown is like a big mall in itself! I stayed at the Crown Plaza and it was just the coolest! You can catch a train to Mall of America, which is pretty awesome. It has its own amusement park right inside! They also have the American Girl store there, your daughter may not be old enough to be super interested, but maybe! They have a Lego store there, which both kids would probably have a blast at.
I've been to Milwaukee and Madison a few times. Madison has some really gorgeous lakes. There's a couple of cruise companies if you want to spend a couple hours on the water. They have dinner cruises and things like ice cream social cruises that the kids might like.
The Dells have some cool stuff. I honestly didn't get to do much when I went, we were only there for like half a day, but they have this really nice horse & carriage ride where you can see the rock formations and stuff. It was pretty interesting, and the horses are beautiful. They also have stuff like Ride the Ducks.
Have a safe trip, and have fun!