I've been thinking about the same question with regard to koteoroshi (our equivalent of kotagaeshi). Munetsuki koteoroshi is on my next test, and the group that will be testing has been practicing it with resistance. I can consistently get the throw to work against resistance, but it's a kokyunage--I'm not throwing uke by doing anything to his wrist. I can frequently annoy my training partners as uke by coming in close, getting my elbow under my wrist and regaining balance, and they find the throw difficult from this position.
I said to one of my sensei "This throw only really works as a kokyunage" and of course he asked me to demonstrate. He let me get into the balance-regained position from which I normally block it, and then took my fingertips straight into the mat, the rest of me naturally following. It was very convincing.
My conclusion from these experiments is that it's good to be able to throw by unbalancing, but it's also good to have options when this doesn't succeed. At higher levels uke has a lot of options for regaining his balance and trying to resist or reverse nage, and nage had better be prepared for them. You may also need the wrist technique if the initial attack was unusual, especially if it was too close to your body or you didn't have space for a good turn. When our dojo is crowded for a seminar the wrist part of koteoroshi increases in importance because that's all there's room to do.