I think what is causing me difficulty in understanding this wrist thing is that it seems no matter what I do at the beginning my wrist position during the upward swing is going to be totally dependent on my intended contact.
If I am hitting a slice serve my wrist must be positioned a certain way to allow the racquet face to slice the ball more toward the right hand side (for righty server) than if I am going to hit flat where the wrist is going to be in a slightly different position.
In my personal experimentation the things that have mattered are grip and swingpath. The wrist for me is pretty much along for the ride. I have gotten some nice boost from working with adding more supination before pronation, but I think that's not really related to this discussion. I'd be interested to hear others theories on how the wrist position at the start could effect the larger forces later in the swing.