I've been thinking of taking a road trip in my BRZ as well. I am from Vegas, and I was thinking of a trip like this.
http://www.us-parks.com/1-week-grand-circle.html
It's a loop from Vegas to Arizona, and up through Utah, checking out 5 different national parks based on the grand canyon. I know you aren't doing a loop, but maybe you can use it as an idea for when you get to the Southwest region, or when you leave Colorado