No idea how smooth it is but if you’re coming all the way from NE you might as well drive the extra 2 hours to 61 Kartway and actually race. The only way you’ll get on the Marshalltown track is during one of the autocrosses. Besides autocross, karts haven’t been on that track in 10 years. I’m not sure if the autocross uses the entire track or not.
You could come to 61 Kartway practice all day Saturday, race Saturday night, spend the night and practice all day Sunday to make it worth the drive.