There's no point to trying to redo the interface art unless someone at simplifies it at the Source Code level. At the moment, every image you see is unique - there's zero duplication of images, even where the images are identical (such as scroll buttons, checkboxes etc.), the files are separate.
The ideal solution would be to use some sort of Alpha mapped TGAs so that the base image had a space for the buttons, and it just got placed on later, or an interface that was entirely generated, either through 3d rendring or repetition of images (borders, corners, etc.)