Info about the curlicue fractal . I didn't know of it either until I read that site.
The problem with Quaternion Julias isn't really the fractal code itself, that's just a more complicated version of normal julia code. In Quaternion Julia's you have q = r + ai + bj + ck instead of z = a + bi. What I have problems with the actual rendering of the fractal. Did you ever try applying the normal julia code to a ssc grid? It doesn't look like a julia fractal at all. This also seems to be the problem for the quaternion julia. My idea was to actually make a 3d block of points and color code accordingly, but that's very slow (a block of 100 x 100 x 100 points needs a N of 1000000). I think I shouldn't go over N=2000, so at best I can have of 2000^(1/3) points per side. That means only 12 points per side and that isn't a accurate as I want it to be.
I could solve this problem with a kind of 3d line scope, somewhat like the 2d-ones used in for example el-vis' fractals.
You still have the problem of the blending then, because replace would leave you with black points covering the screen and with maximum blend you can see the points on the other side of the fractal and that would make it look really weird.