One thing that might really get people to purchase a drawing is the ability to change line colours. Imagine all the colourful patterns! Have you plans to add this?
I don't really have many plans to keep working on this machine, but I do hope to add new machines (with different controls, and different possible outputs), so I'll definitely keep that in mind :)
I've been thinking of it a different way, though. The option exists for people who want to manage the printing themselves, and it's a much more economical version.
The fine-art prints on my project start at $99, and while the profit on that varies by where it's shipping to, it's always more than 20 bucks. It doesn't cost $80 to produce and ship a 12" x 18" print.
Put another way, you're not paying for an image download, you're paying for the creative energy (not to mention time) that went into producing this tool.
That said, you're not the first person to bring this up, so clearly the messaging could use some work. I've lowered the price to $5 while I figure that out.
I just bought a download for $5. I don't know if 5 people would pay $19 vs 20 would pay $5, but you just got five dollars more from me that you would've otherwise :-)
Fun fact: While any combination is possible from the "randomize" button, it uses weighting to try and come up with pleasant/interesting combos more often than not. I'm quite pleased with the results.
Edit: I contacted you via the contact form at Tinkersynth
This project was actually meant to be for plotter drawings originally, and the SVGs it produces are plotter-friendly (all the occlusion is done mathematically, not using fills or masks).
Perhaps someone in the near future will make a similar art cover using graphs of exoplanet transits.
The reason is that the experience really only works when you can see the art while you're tweaking a parameter, and there was no way to fit both the art and the controls on a phone screen at once. I had them stacked, and scrolling up to see what a control did was a miserable experience.