mimiihu: cranioscopical, i think this is still not it but it has a lot of features. maybe you can find some useful. it's shareware, tho.
i couldn't find any other solution without installing and testing.
another half-solution you have is to increase vertical spacing and keep horizontal spacing, for example, so you can have separated horizontal groups of icons. (or the other way around).
Hi, it's very nice of you to offer those suggestions. I appreciate your input.
I've tried Desktop Icon Toy and it's getting there. Given a few more iterations it may be the answer I'm seeking.
Also, thanks for the suggestion about differential vertical/horizontal icon spacing.
Meanwhile I've posted a request in the coding snacks section, so we'll see if anyone there can help.