[Lerc]

I'll add to that the possibility of adding a layer similar to http://www.contextfreeart.org/

It occupies a somewhat similar space, (I believe it does not provide composition operations). Having the ability to define shapes as a probabilistic combination of other shapes gives you a massive variety of possibilities.

something like this would allow for a good variety of base imagery which could then have the layer I posted in the previous comment come after.

Check out the context free art gallery for some amazing (not very logo like) images

http://www.contextfreeart.org/gallery/