Let's say I have a scene with 100 green marbles and 100 red marbles. Would it make any sense to combine all the green into a single mesh and all the red into a single mesh?

First, does it make sense, and second, is there some simple way of say:

loop over marbles:
  We've got another green-marble
  Add it to the existing green-marble mega-mesh.

The marbles aren't going to be moving around independently. If they move it will be as an assembly anyhow (i.e. move all green marbles to the right by 10).