Glenn,

What if it isn't so much observation, as the most basic logic, like if space expands, why doesn't the speed of light increase proportionally, in order to remain Constant?

It essentially assumes two metrics, based on the same light. One on the speed and one on the spectrum.

So how are they related? If the speed were the numerator, it would be a tired light theory, but as an expanding space theory, the speed is still the explicit denominator. The metric against which this expansion is measured. As Einstein would put it, The Ruler.

It's along the lines of saying that our theory is great, but it only works if 1+1=5, so lets just assume 1+1=5 and go with it.