A very nice write up, I will admit I have not gone through all of it
yet in detail. One thing to consider is that CCD have a read out noise
of around 10 electrons, whereas this noise level will not greatly
effect the signal to noise when looking at 400 detected photons with an
noise level of 20 electrons it will start to dominate in darker parts
of the scene. For instance by the time you are down 5 stops from full
white the readout noise will be larger then the photon noise, by a
small amount.

The idea of using non-RGB filters is sound and a number of CCD sensors
have used filters more like C, Y and M. Why RGB is used on digital
cameras I am not sure.

Scott