Another good choice might be Mackinac Island probably staying on the mainland at either Mackinaw or St. Ignace. This is right at the junction of lower and upper Michigan. Nice touristy kind of place and the island is a true delight. Might suggest a Saturday-Sunday pair of dates since it's a bit further, but well worth the trip, I think.

Of course, I'm prejudiced, but Peoria is a good choice given all the things I've mentioned in terms of things to do. One thing that might make the August date better is the availability of Saturday afternoon rides on the Spirit of Peoria Riverboat. They end September 1st. The cruise is a delight and well worth the visit as it's one of the very few paddle wheelers that uses the paddle wheels as it's only power source. Ticket Prices are $13 for ages 13-54 and $11 for 55+.



Also neat would be the wheels of time museum. A very interesting and inexpensive site to see. http://www.wheelsotime.org/