In KY, at least stop at Bernheim (it's right at I-65 exit 112, south of Louisville but before Elizabethtown). It has a fine maple collection, with many plants dating back to the early 1960s, along with an awful lot of other fun plants in the arboretum.

Here is a link that might be useful: Bernheim Arboretum

Yes, Bernhiem is beautiful and very user friendly. I was lucky enough to visit it a few years back. As a bonus, you can cross the road and tour another Kentucky icon: Jim Beam Distillery. There's a beautiful old Ginkgo near the original house, which is now used as the visitor center. It gets better--you get to sample the product, even their top shelf bourbon. It's no Woodford Reserve, but its not bad.

If you can jump over to Birmingham,AL they have a great Japanese garden with several mature maples at there Botanical Gardens. Its free and even has a Bonsai collection. The area is near a nice outdoor shopping area which the wife and mother in-law like.

The japanese garden has a real tea house shipped over from Japan. Great dry sand bed with hugh boulders (not sure what they are called). A dry creek and gorgeous small lake. All of them are lined with gorgeous maples. They will be dormant by then, but i imagine even then the branch structure of the mature specimens will be nice.

Atlanta has a nice Botanical garden with a japanese garden. But not nearly impressive as Birminghams. It does have a great tropical garden with many simulated enviroments from south america. Beautiful orchids.

Mike

Thanks everyone for your suggestions. I think I will enjoy the trip more than I thought, now what type of rental car to get... :-)