I've enjoyed visiting the Cathedral of the Plains (Victoria KS); its beauty is amplified by its small-town location.
If you stop at the Archway in Kearney NE, there are some Lincoln Highway points of interest outdoors (meaning you can view them even if you don't want to pay admission for the indoor exhibits).
You already mentioned the SAC Museum and the Doorly Zoo; those are both worthwhile stops.
If you like the SAC, you'd probably also like the Cosmosphere, which is in Hutchinson KS (not far from Wichita).