Printer woes solved! First off, thanks to all my friends that patiently listened to my ranting about my (now headed for eBay) old printer, my flailing search for a new printer candidate, and my general digital art frustration.
My old printer is extraordinarily inconsistent, and out of warranty. But as far as I could tell, buying a new printer with equivalent ink would mean plunking down another $400 to $800, which I can't stomach doing right now. I always love printing on matte watercolor paper, but Epson's less-expensive printers can't accept media that thick. So, I felt like I was out of luck unless I spent a ton of money on yet another printer...
But, nicci pointed out some great opaque, double-sided, matte media that will feed perfectly through those less-expensive printers. And, my research on archival ratings revealed that both the ink and the media were much more archival (fade-resistant) than I had expected, which was a tremendous relief. I never thought I'd find something I like better than watercolor paper, but... yay!
I'll put my old printer on eBay... perhaps someone else can convince it to behave better than I can. I'll sell the extra ink carts, too, which are worth quite a bit. Between the two I'll probably make more than enough money to cover the new printer. :D
The pic shown on the right here is a scan of output from my new Epson R260 printer. The colors are great... really rich teals and greens which I couldn't get out of my old printer. The dots are completely invisible as far as I can tell, resulting in a smooth continuous-tone which is perfect for the color gradients in my work. I can get high-capacity cartridges for this printer, too, which makes the ink that much cheaper per milliliter.
So. My master plan for this branch of my artwork is to try doing one of a kind pieces... 1/1 instead of 1/12, perhaps with some overpainting to further differentiate the originals. I'll see how they sell. I can do the twelve-way color shift in the open-edition reproductions instead, at any size, and I can make ATCs too. And, perhaps I can get some frame shop galleries to pick up my prints in their inventory if eBay doesn't work out.