I'm picking up a M3 from Minneapolis and driving back to Hays, KS on Sunday.

Anticipated route is I-35 south to Des Moines then get
onto I-80 west until York, NE, head south on hwy 81 to Salina, KS
then west to Hays, KS..

Any better roads for sight seeing that I might detour on for a 100 miles or so?

I want to be back home by 9-10pm or so..mapquest says about a 12 hour drive..

Thanks....

Just south of Des Moines near Indianola you can pick up Hwy 69 south. It goes all the way to KC. After about 5 miles south of Indianola is gets a little curvy and rolling hills. You are never too far from I35, so it is easy to get back on the big road if you need to. There is also lots of construction on I-35 in southern Iowa and northern Missouri so you won't loose that much time while on the two lane.

This is good diversion in Kansas.
http://forums.bimmerforums.com/forum/showthread.php?t=439487

Looks good.