@sambrookjm: Unfortunately I think I am doing something wrong as your script just makes a large circular gadient centred in my image.
@RobA: That is actually the approach I have been working on, but I am none to keen about fiddling with the nodes as Inkscape has a tnedency to crash when I start working on things like that. The other thing I noticed is that I would need to create a 'mid-way' guide contour if one of my shapes is especially complex. In the test image I provided the inner shape has a curved 'indent' that needs to be guided to the outer shape, else one gets high contrast edges/ridges forming. I hope that makes sense.
Recently I have been looking into using Wilbur. I just wish Wilbur allowed the use of layers, so far I've been exporting as greyscale bmp's and combining them in Gimp as layers.
Anyways, back to it for me.