Ah, Substrate is a screensaver: https://www.youtube.com/watch?v=dCCVgBOVD0E It avoids the loose ends by starting seeds directly on existing lines. I was acting like you'd heard of it because I've seen it mentioned a couple times in the context of history of procedurally generated art. https://procedural-generation.tumblr.com/post/124657726768/substrate-2003-shortly-after-the-turn-of-the
Having played with the code more, now I understand that the objects are rendered in one at a time to give some appearance of depth. It does look like there's a setting for number of starting seeds which gets used on a few objects.
It might be interesting to produce some symmetry by having some objects which place two seeds at a time, symmetrically. Maybe that would be a solution for getting more face-like things to appear.
Anyway, I'm enjoying poking around in your old project. :)