I'm so behind on comments. But this story was so awesome I had to say something at a time approximating currency.
I don't have an "official" top EP stories list as some posters seem to, but I agree with MacArthurBug. This story is on definitely on it*. Both for the story itself and the masterful reading by Pip Ballantine. I enjoyed it much better than "Instead of a Loving Heart" which was complete meh for me; given that I also loved "The Yeti Behind You" on PodCastle and "This, My Body" here, I'm going to declare myself a Jeremiah Tolbert fan and consider "Loving Heart" a fluke.
I'm really interested in what the rest of the world might look like, or what it looks like now after the Arties' rescue. Although improbable, I liked the idea that the gengineering kits were able to be used by people who didn't know what they were doing and couldn't even read the machines; it's nice to think that science can be artful, or that one can intuit life from design principles instead of only the other way around.
There might be some Arties who didn't have such an extreme ache to create, who found more support from their elderfolk. Most of these kids can clearly stay out for extended periods of time without their elderfolk noticing/punishing/looking for them (they waited three days for Niles to return with the kits); the group the story is focused on could be made up of the more neglected among the population. Art supplies are clearly available somewhere for Niles to steal; perhaps this is a band of underprivileged Arties. They don't seem to go to school (unless I missed something). Brainiacs and Thicknecks seem to also rove in gangs though ("rove" in the Brainiacs' case meaning "hang out at the library").
Or, since we are getting the story from the underdog's perspective, the elderfolk's problems might stem from simply not understanding their charges' needs, rather than from malice outright. These kids don't fit into the "system," and what are their parents going to do about it? They can't "fix" them short of recycling them or telling them to suck it up and deal, it seems, and giving them an appropriate outlet for their talents seems beyond the adults for some reason. Or perhaps the elderfolk simply have no idea the Arties have this craving to create, and think their drive is just youthful indiscretion which needs to be trained out of them. So the elderfolk try to keep a leash on their Arties and have the Tinmen clean up when they color outside the lines. From the Braniac's description of boredom, they might be in a similar position of not having enough to occupy their considerable talents. Adults often just don't know what to do with a superbly gifted child. There is unfortunately a very real struggle between making sure a gifted child gets the socialization they need to survive in the world, and giving them the opportunities to exercise their talents to the fullest. So Arties are stupid and can't fight; Braniacs can't think outside the box and don't get out much; and Thicknecks, I'm guessing, are big dumb lugs with no vision. Who knows what Skinnybois are/do.
From Zinger's opening plot contribution, it seemed like some of the Arties might have had more stable homes. Zinger mumbles something about his elderfolk not wanting him around, and from the context it seemed more like he was a young aspirant trying to get in with the "punk" crowd but didn't have enough street cred to really cut it at first. But they seem to all band together when it's time to rescue Niles.
I kind of agree that the exploding seeds were a little random, but we're seeing this through an Arty's eyes. They apparently remember their birthplace, something which for us ordinary humans is extraordinary, but to the Arty's it's a) normal and b) they care more about getting Niles back than anything else in the scene. They don't even stay long enough to hear the adults' explanation for why they need Niles, so we don't get to hear it either and have to just guess. It made sense to me within the context of the narrator's POV.
*For context, "How I Mounted...Saved...Sniffed" is already on the unofficial list, and I'm retroactively adding "Friction," "Mayfly," "God Juice," and "Conversations With and About My Electric Toothbrush" off the top of my head.