Michael,
Working with and modifying the toys seems like it would be a neat intermediate step between simply playing with them and building models of them.
Still, it would be neat to actually have kits of the Autobots and Decepticons to build. It would be even neater if they were in a constant scale and could actually transform.
Failing that, it would be neat to make the robots by starting with a kit, cutting it up, and making the robot parts -- sort of semi-scratchbuilding the robot figures.
I wouldn't mide taking it a step further and making up new figures based on some vehicles that haven't been done yet. For example, I think an Autobot that transformed into a Cessna 182 would be pretty cool.
Regards,