One of the other interesting things is that while CBS may not have all of the source files for most of the VFX shots: The original artists do have many of them, and would likely offer them up in a heartbeat. The original 3D models and scenes for DS9 and Voyager are incredibly detailed, and would be more than adequate in HD. In many cases, it'd just be a matter of loading up the files, changing the output resolution, and mashing the "render" button.
Indeed. I think its TrekCore that has some HD images of re-renders of the 3D model of Voyager used on the show. They are so detailed, you can start to see the where the 3D artists copy/pasted the same empty sickbay stock photo in various places around the ship to show there is something inside the windows.