Personally, I'm a big fan of HSB for this kind of thing because you can get a smooth walk through the rainbow.  I think it would be fun to get a range of colors up on the screen at one time -- try coloring them according to position in the spiral and then  changing those colors, for instance. Or try not clearing the screen between draws and using an alpha value to make them mostly transparent. Could be cool, could be not so much.

I'd also try rotating the spirals in opposite directions when there's an even number of them.