Keith, Excellent post, but I'd disagree with you on one point, namely -
So if we climb at constant CAS the drag will remain constant (if we ignore reducing mass)
If we climb at a constant CAS, the EAS will be steadily reducing, and drag will be REDUCING. Drag arising from the Low Speed Polars is related to EAS, not CAS. (This is actually beneficial to the climb as thrust is also reducing as we climb).
All of this is valid until we encounter Mcrit, as you've pointed out.