Oh yes, I can see how that would be beautiful! Of course I don't understand dithering (or maybe the filters either). But I can see how pretty it would be.
It would be interesting, if someone had access to a state of the art machine, to install Inkscape and try something like that. Just to see how far you could get.
When you apply the gradients, and you mentioned having a couple of dozen gradients, do you apply them manually or visually choosing the right place for each one? Or do you use some kind of script or automatic way to apply them to the best rectangle?
For the one "at least" with px.png screenshot, I'm curious about the shadows behind each rectangle. When I extrapolate that small sample to the large lighthouse image, I wonder would those shadows even be noticable? Because of how our eyes work when looking at very small things, I guess it might be possible to give the effect of those shadows, in some other way. Maybe save some resources?
I don't know how the shadows are made. But if they are also little rectangles blurred, it might be possible to use a simple, 2-node blurred stroke, to represent the rectangle. At least save a couple of nodes for each shadow, would cut that much number of nodes in half. Or are they made with drop shadow filter?
Well, I know I only have simple ideas. I wish more advanced Inkscape users would participate and give you better feedback. But I hope they won't be so afraid of the new forum, and maybe will visit more.
(Changing the subject, I'm worried about your cache of filters on Open ClipArt. And I'm starting to doubt their claim about being under ddos attack. Because after all, any good webhost can block ddos attacks. Have they told how long before they can restore the site? I thought they had some connection to Inkscape project, but I don't remember who. I don't understand why the Inkscape project has not investigated more.)
(Maybe you could host your filters on your website?)
Edit
Just tried to visit OCA. They're asking for donations for "protection" which just seems strange. I certainly would like to hear the truth....