I only do work on my layout but I will share ideas with you. I would not try Superstreets in any form: a scale tractor or even a 1:43 or 1:35 one will be too small to carry a motor/gears sufficiently torquey to assure smooth scale running at tractor speeds, and it would too short to have good electrical pickup.
Two approaches come to mind. First, a farm field has rows of plants which would hide a slot. You could build a mechanism that had an oval slot from which projected a peg that dragged an otherwise unmodified scale tractor around the field, and drag that with a mechanism from underneath. I've seen youtube videos of a bulldozer and construction site done like this. It looked like it worked well.
Second, you could use magnets. The field surface would be made of 1/16 inch plastic. Imagine a 2 foot diameter plywood wheel just under the surface of that plastic, that rotates with a magnet at one point its circumference and a magnet mounted under the front of the tractor: it will just drag the tractor around in a circle - not an oval but you have the basics. 2 RPM gives you about 7 scale mph. If you want an oval, just use a bicycle chain around two large sprokets and mount the magnet to the chain. Either way, a "Pellet Stove Auger Gear Motor, 2 RPM, 120 volts" (Amazon has them @ $60+ ) or a motor made to rotate a disco mirror ball will work well to power it. This will work. I've got a prototype working for another application and I have still incomplete plans to use it to power a construction site/farm on my layout (I know I want to do it, I know how to do it, I don't know where I will put it, though -- I'm running out of real estate). You have to use tough plastic for the surface - that made for roof flashing is really good, and then mount it so it is rigid and held in place firmly: the magnets clamp from above and below with surprisingly high levels of friction. But it will work, and in fact with a little creativity in the use of the chain and sprockets you can make the path wind over fairly complex routes.
