These were display layouts so spurs were setup to demonstrate operating cars and accessories. The cars weren't ment to be moved so the "dummy" mainline/double tracks were used for scenic interest (like to show the 450 signal bridge). Also, a lot of times the spurs that were connected to main tracks werent powered directly. The D-131 posted above used a manual switch and there was a insulated pin in the center rail preventing a direct movement into the spur. Some modifications to the plan are necessary for making these more operator-friendly.
Also, one note on the D-27 Fastrack plan. The down grade is very steep and i recall from the CTT article that the track on the start of the grade had to be physically bent downward to have a smooth transition. Care would have to be taken that a smooth transition can be made because you can't bend Fastrack like that. Use of transition tracks and a piece of tubular may be necessary in that location.
Peter