I am so happy to discover this forum (I'm exploring the various forum sites like a gourmet approaching a feast with a lingering taste and reflection of "this" before I move on to "that." I very much look forward to meeting you, Sensei Canna at the next summer camp!
For whatever it's worth, I like to think of the movements in the Uechi-Ryu curriculum as conceptual rather than discrete units of "you do this and I do that in retaliation." As everyone subscribing to this forum seems to be pretty hip to the verities of real combat, we know that choreographed material is, if taken at face value, just that - dance. However, if we see the movements of the kata as paradigms of energy vectors then each movement becomes rich with implication for bunkai interpretation. This is usually amplified by taking each movement in concert with the movements preceding and following it. Thus, the "pull back" from Sanchin strike can be not only an elbow to the rear, but also a grab pulling something back to "borrow power" from the opponent and augment the strike that you're sending out with the other hand. As such it represents exercising simultaneous independent action of the hands, an activity which if close range combat is to be given more than lip service in our art, must be fully researched...ie, are all those one armed exercises we do in Hojoundo really implying that we should fight with only one hand? Obviously no. It also introduces the ideas of Yin and Yang into the form, ideas that become very pervasive and important in all subsequent kata.
Similarly, although I personally enjoy conditioning the fingers, I don't confine the interpretation of the nukite strikes to what is "screwed on" the end of the wrist. I see the nukite strikes as conceptually teaching me how to stike with relaxed (using the concept of "Sung" meaning explosive/elastic power rather than "limp"), grounded, and totally committed power that uses the elbow as the origen of the power line, as much absence of tension in the antagonistic muscles (particularly biceps) as possible, and use of the back as the foundation and stabilizing structure of the attack. With those ideas in mind, it really doesn't matter what form the hand takes. Could be a nukite, could be a fist, a shoken, a palm heel, or, if I somehow break my hand and still have the opportunity to hit you, could be my wrist. For that matter, if you block my strike, the same lessons learned in the Sanchin strike prepare me to effectively convert the energy initiated in the nukite into an elbow attack, a "leak-over" or "under" your bridge arm into a side of the hand strike to the bladder, etc.
As Sensei Steve and Evan say on their excellent tape series, don't take this stuff at face value, there's much much more to it.....and less.
Best to all,