I've tried graphite on paper before, and it works quite well. The only problem is the delivery system, would like to see something better then a pencil, ... maybe out of a spray can, so you can spray it on ... a stencil of some kind with the pattern for a circuit.
Now think of those implications, how cool would your models be then, how easily could you incorporate lights, or sound, or other small electronic things....
Graphite powder makes for a great conductor. There is also copper foil that can be used and cut into very narrow strips, using conductive tape to bridge connections. I used this method when I designed my own electrostatic speakers. If you take a large piece of plastic that does not conduct electricity, and put it between two pieces of aluminum foil, you can calculate the square area, and make your own capacitors. It would not be hard to make a paper box, with predominantly paper components, not use any wires, and have LED's, switches, and a battery box, completely scratch built.
If it over heats, and bad, it will burn up though, and very fast, which is why you don't see this much.
It would make for any interesting model, a simple Integrated Circuit, made out of paper, with graphite, or copper foil traces, and arsenic doped plastic bridges for diodes. Making gates would be, well I haven't tried that yet. Nand gates, etc, would be cool to see modeled at such a large scale.