nice posts :) just a few comments, if you don't mind:
regarding part 1: I think Nick mentioned somewhere else a nice way to circumvent major client changes - by having light (and shadows) on separate layers. It's a bit more complicated to work like this, but it may save a lot of time in the end.
regarding part 2:
If you think about it matte painting is almost opposite the full CG pipeline. In the full CG pipeline geometry has to be created first. Then it has to go through the process of being textured, lit and rendered before in can even be considered an “image”. With matte painting, the image is created first using photos and then the geo is created to catch the projected matte painting. A lot faster.
Not entirely true; Most people who haven't worked on a lot of high profile projections think that you do the matte first and create the geo later to match it. In reality it's the total opposite - geometry is created first, tested with concepts and then matte painting is made to tailor that geometry. Why? Because of two reasons:
1) It's much easier to plan the camera movement ahead and do the matte knowing exactly which areas to cover, rather than patch & fix it at the end.
2) It's much easier & faster to paint over geometry than to match geometry. The result is relatively the same.