Thanks Rob. I have felimage, but I'm looking for something a little different.

I like the texture of GIMP's solid noise, but not the regular spacing of the curds.

Here's an image that I hope will illustrate what I'm looking for:
Click image for larger version. 

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The left half is GIMP's solid noise, and the right is done with felimage noise. For the felimage side, I twiddled with the settings until I got about as close a match as I could get to the GIMP side. I like that the curds don't line up, but the gradient from dark to light is much smoother than with the solid noise.

Inset on the felimage side is close to what I want. It's built with several iterations of the felimage filter stacked up, with assorted adjustments to scale each layer's range and density. If I experiment a bit more, I think I can get what I want, but it's slow, as in S L O O W. As a manual process, it took about forty minutes to build this example. I'm working on a script to do this, but it will still be slow, requiring five or six separate invocations of the felimage filter.

I was just hoping some clever person out there had come up with a more efficient solution.

Thanks again,
Hugh