We loved Hohenwald, right on the Trace. Great, free campground. Merriweather Lewis' grave nearby, a great coffee shop downtown, very good used bookstore, a surprisingly good museum and re-creation of Lewis and Clark's fort. Well worth the stop!
We also really enjoyed Natchez, MS. It is just amazing how deep the path is from the trace just north of the State Park. Also, a great coffee shop with wifi in town. I don't normally note coffee places, but these two were outstanding.
I remember our first drive as very relaxing, but we did a bit of the drive last year and found it quite bumpy. Is that just a small area, or did frost heaves affect the drive for a longer part of the Trace?