I quite agree with you about the pricing of Cochin. Frankly, I don't understand it myself. But I have noticed that, when good earlier material is offered, it still gets good prices - mint or used.
I've commented elsewhere that part of the blame may be with new, unsophisticated collectors coming into Cochin. They've been told that they must buy only mint unhinged. It's easier to find the later material in that state, so that's what they concentrate on.
Still, not all the earlier items are unappreciated. I had to fight very hard to win this cover (and another with a similar franking)

on
ebay recently. I don't think the competition was for the 3rd Raja 2¼ Anna stamp, either.