I've wondered if i could join in to your project to help 3dmodeling. Im not a professional 3d-artist, so I have tried a little with mannys head to see, if i can handle it. The original model is very simple. Improofing poly count should be no problem, but the meshes are all made with triangles, so i built the whole head from scratch, using quads. makes further improvements easier.
At this point, the Head has 136 faces. The mesh is still very simple. With a sub surf modifier 2x applied on it, it makes about 2200 faces. Extrapolated to the whole model, it makes up to 10k-20k faces. maybe more, i don't know. how much detail would be needed for the main characters. Is 20k ok, or already to much? or maybe we could get much higher? I have no idea.

Here is a quick render. The shape needs a little bit more tweaking. overall, i tried to stay as close to the original as possible. i think it would change the mood to much if there are added details wich aren't in the original model. of course its a matter of taste


