Ah, I should have read post 2 and 3 more carefully! It's making more sense to me now. I find the results are better for zoomed-in sections, since, with black borders, the highlights tend to sink into the border junctions in the main shapes and interrupt the illusion of shape a little bit. But on the edges, I now have nice balloon-like structures, just as I had hoped to!

One thing I noticed is that I had initially misread part of your formula, but gotten similar results... You highlight the cell edges with "min/min2", while I set mine up based on "min2 - min".
I suppose it's a similar idea either way. with yours, value approaches 1 when the distances are the same, and with mine, value approaches 0.

Anyway, here's an example of today's tinkering after your hint.

There is no right or wrong version. Dividing sort of scales wall thickness with cell size; while subtraction sort of sets a constant boundary thickness. Either may be more appropriate for any given image. I think of it as a design decision.

BTW, one welcome side effect of me being a bit vague (about computing final colors from the raw values) is that some of you might discover yet more interesting variants that would have never occurred to me.

Now let the trap position move and watch more hidden structure coming to light.

The example pictures with cobweb like cells inside the main cardioid got me thinking. Is it possible to make such webs simultaneously visible everywhere inside the Mandelbrot set? That would mean choosing an orbit trap position per pixel.

It may be kind of possible. Here's an experiment where I took the centroid of the entire orbit as the trap position for coloring.

I guess a more correct (less approximate) way of doing this would be to identify the attracting periodic cycle, and use the centroid of just the cycle's points. But even then I am not sure if the pattern could be spread beyond just the main cardioid. Outside colors are pretty much meaningless here.

Really cool stuff. Here's a result of applying this orbit trap to a small Julia set.