Something I found interesting from that last formula... I couldn't really get images as nice as yours (it's sensitive to escape radii and coloring algorithms and would take too much fiddling, I think) but I noticed how BIG the julia's were, compared to other formulae.

One thing I like to do is apply circle inversion to julia sets to see the details in a different way, and this reminded me of an already-inverted julia image.

So here's what I got when I inverted these. For every C value, inverting would result in these repeated patterns to infinity, at different angles depending on C.