I don't know virtually anything about gimp, but how would wallpapers following these ideas be?
1. simple but not plain blue background with the Vector logo, along with the text: "Stable, Quick, Vector"?
2. different OSs depicted as huge lumbering ships and Vector as a speedboat?
3. a twister filled with all of the different things in a standard Vector release such as KDE, OpenOffice, Konquerer, etc with the small end going into the logo, "How on earth did we get all this stuff into such a little package?"
4. an old computer, an Eee PC, or something: "I may be slow, but I can still run Vector as fast as the rest".
just some ideas, based on what I know of VL so far.