I spend a lot of time in master documents. The Master View Navigator panel
allows me to click on a section (which is actually a file) to Update it, Edit
it, Insert or Delete. But after I update it, I want to look at it. One more
option -- to go to that section in the master document -- would save me hours
(over the course of weeks working on a book) of trying to find the chapter I've
just edited.

Formatting changes in the master document mean that changes you make in the file
you've just updated don't always look as you'd expect. You want to see them in
place. Right now that means hunting. Lots of hunting.

Less important, but on the same subject, would be something that allows you to
click anywhere in the text of a master document, and then see the section
highlighted in the master navigator. Then you wouldn't have to hunt in the
navigator to find the file to change.