Well you asked a very good question and I think the answer will change a bit depending on what part of Iowa you are in. The southern part of the state is nothing like the north. Spot & Stalk is a tough game in the south because of the rolling hills and heavy timber. In the northern or mid part of the state, things seem to flatten out and spot and stalk is a very good option.
I'm sure you know the legal requirements of the state and in reality, coyotes have very little protection here. About the only thing I can think of that protects them is you can not use a light in the state and of course trespass laws. Other than that, you can chase them with hounds, shoot them with the .22LR to the 50BMG, call them with electronic callers or hand calls, hunt them 24/7, hell you can even chase them through sections with groups of trucks and run them over to make the kill.
Of course all this pressure makes them terribly nervous critters. If spotting, I tend to look into the middle of the sections as coyotes I believe try and hunker down in little dips and draws that are not visible from the road (your challenge is to find a way to see back into these areas), fox on the other hand I've seen laying up sunning as close as 15 yards from the road (they ain't that smart).
If the bet was what coyote hunter will see more coyotes in Iowa after crops are out, I'd put my money every time on the guy spotting over the guy calling. I know of guys who spot them and consistently kill up to 10, 4 or 5 days a week with snow on the ground (I'm definitely not one of them LOL). So I guess what I'm saying is when people tell you that you will see very very few coyotes spotting from the road, check and make sure they hunt in Iowa. LOL
Looking for tracks, obviously your best bet is going to be after a fresh snow, but you should still be seeing plenty of tracks on fence rows, field drives, and on the edges of gravel roads (especially level B & C less traveled roads). If you see tracks heading into a section get out of the vehicle and check. I often see deer and coyote tracks next to each other, as well as pheasant and rabbit mixed in with coyote tracks.
For scanning I drive 25-45 or so and just keep looking in the fields and try to ID any spot that looks out of place, or the right size. Also keep an eye out for fresh tracks going in and out of sections. So pretty much one eye out in the fields, one eye looking for tracks, and drive by feel. I don't stop and scan every section, I scan sections that look likely to hold coyotes, have been proven to hold coyotes in the past, have fresh or several tracks going in them, or have a likely looking spot (as seen in Kirby's pictures)in them. I usually cover (average) 100 miles an outing. And the name of the game with this type of hunting is OPTICS IMO. You spend a lot of time looking through glass and poor optics will cost you coyotes, cost you time and money, and after a short amount of time drive you nuts!
Your approach on calling sounds ok to me, as long as you are getting away from the vehicle enough that the coyotes cant see it. Also be sure that you approach your evening calling stands as carefully as a daytime one. I know in my part of the state the snow is very crunchy which a coyote can key in on from a ridiculous distance. I have not hunted coyotes out of state so I won't speak from experience but from what others who hunt Iowa and out of state tell me, ...now let me phrase this right..... Your call in percentage will be less in Iowa than many other states for a variety of reasons. So don't get discouraged to quick. How many times have you been out, how many stands, how long of a time span?
Good luck and make sure and report how you do.
Mahamari