Not really on the path you are taking, but if you ever need to pass through the panhandle of Idaho, instead of taking the interstate from Missoula to Spokane, go over Lolo pass and drive highway 12 along the Lochsa river. It is a gorgeous drive until you get close to Lewiston. From there you can head north to Spokane.
If you take this route in the spring so you can be treated to whitewater rafters flipping their boats on class 5 rapids (I've been on the Lochsa swim team before,lol)