I've been kicking around the idea of the disk being used for time telling purposes, possibly a timer of sorts. Think "sundial" and imagine the disk being mounted on a post protruding through the center which would function as the dial. The user could then spin the disk to a fixed point (say the beginning edge of a lobe) and the shadows progression would indicate the amount of lapsed time.
While this doesn't explain the ornate nature of the design, it's association with the sun could have something to do with it.
I know this post is more about form than function but I wanted to throw the idea out there.