>.....I wonder how one of those after-market >focusing screens with a split-image rangefinder might help add >to this experience.
I installed a Katz Eye on my D300 for just that reason, but was disappointed. The Katz Eye was nice, but no faster or more accurate than the factory screen of the D300.
In comparison, the factory screen of my D700 seems slightly brighter and easier to focus manually than the D300. Probably because of the slightly larger image. I don't have any problem focusing manual focus lenses on my D700.