If you're into Lincoln era Springfield and have time to burn you could drive to New Salem. From what I remember its kind of a replica of where Abe lived in his younger days.
Or if you like architecture there's a cool Frank Lloyd Wright house/museum downtown. Don't remember the name. Or way on the other end of MO, if you end up anywhere near KC skip the Cinderblock Camaro Museum and go to Liberty memorial and the WWI museum underneath it. Easily the best thing to see in KC for a history guy. And probably for anyone in general (without a lean-to CamaroPort attached to their single-wide.