I'll put in my "two" Cents worth in. My first Penny Suggests, as KJ did: Hwy 136 to Royertown Access (+/- 17.5 miles). This would be along high buffs; which probably would be more visible with more leaves having fallen by then. Less agricultural, avg gradient 2.5'/m, & would give a hard surface shuttle. A stretch that I've not paddled. With an optional take-out @ Chenelworth Access (+ another 2.6 miles, for near 20.1 miles). Or for a total float of near; 22 miles, take out @ Morehead access. Going to Morehead Access would add 1.5 hrs to the float.
My second penny suggests: the Iowa River From Fredonia to Schwaob Access (13.3 miles) @ Wappello; with long sandbars & islands, along lots of public lands with woodlands. Here you'll have a greater chance of seeing the fall colors; as it's 1/3 of the state south of the Maquoketa. Adding on to the boat ramp; just past Hwy 99 @ Oakville for another 10.7 miles. Here you'll pass a series of treelined islands & a National Wildlife Preserve; where you'll spot geese & migrating birds. For those of you who are into or would like to sandbar camp; this section of the Iowa River is known for great sandbar camping. This trip would give you an idea of that choice before commiting yourself to "packing It in".
Sorry, to be so long winded. I just wanted to add to the discussion & help others that don't have a copy of "PADDLING IOWA" by Nate Hoogeveen.
I'll quit already.