Not everyone has the same pile of junk parts to start with. The rules have to be more specific. The following are suggestions and I am sure some of them are flawed.
Most original use for a common device like a floppy, CD, or hard drive.
Best robot (or other specific reuse) using floppy, CD, or hard drive. (or not using a uC).
Most original project using a specific 8 pin PIC (maybe pick the most feature poor 8 pin PIC)
Most creative use for a Junebug, Junebug as prize
On an advanced level it would be interesting to see what people can create using parts salvaged from a single PC MB. Maybe limit it to MB 500MHz and less. This is a bit iffy.
You still have the problem with best and creative being subjective but we all know that going in, and that is what judges are for.
Where creative or original is called for a design already posted to the Internet would not win.
We could also have contests to see who can do the best job of building the same thing. The best PCB from a given schematic or the best tach to measure engine RPM.
I would not mind judging but only if I had access to the entries. It is too easy to fake things.