[JDHill]

Sorry, that would more accurately read:

Looking just at the SPOT LIGHTS layer, we see that there are 12 circular faces on this layer, in a single group with the SPOT LIGHTS material assigned to it, which means they all share the output of the 199W @ 12.7 efficacy SPOT LIGHTS material.

It just means that since they are grouped, they produce a single mesh, and that therefore, each of the 12 circular faces will only emit 16.58W (assuming they're all of equal area). Because SketchUp is so prone to inadvertent material assignment (compounded by the fact that it has both front & back materials), I would generally recommend trying to stay away from face material assignments, and sticking to assignment at the group & component levels, when possible. That usually also makes it easier to understand the model, as it rises in complexity.

Might that have also influenced the red light spilling through the ceiling given that there were lights hiding up there?

Actually, 99.99% of that was purely resulting from the overpowered wattage of the five intended stage & podium accent groups. If you hide those, along with the SPOT LIGHTS and BIG EMITTERS layers, you'll find that the contribution of those 10 accidental red emitter faces is confined almost entirely within the ceiling space -- the main room will be almost totally dark. I have to say almost, because if you use the draft engine, which is quick with resolving direct lighting, and crank the camera EV to 1, you will actually get a few rays of light bouncing around in the scene.