Thanks all,glad it's of some interest!

As for the how to it's really simple,you just have to copy the Power Fractal
and then you set the noise value for your axis of choice to -1 which mirrors
the fractal on that axis and that's it,basically.

Depending on what you want it to be,colors only or displacement only or
both,there are different ways to connect the PFs,if you want colors you
would have to use merge shaders for example.
The above examples have x and z symmetry and use 4 PFs(as a basis) ,for symmetry on
all 3 axis' you'd need 8 PFs.
I've successfully tried this method with clouds,spheres and planes also.
If i have missed something or you need more info just let me know.
Thanks again,J.