UPDATE: I decided to combine XS and Brett's advice. I stripped the glass using what I had readily at hand -- Softscrub cleanser. Results are amazing. All this time, I'd been concentrating on putting stuff on to my glass in an effort to improve things, whin it really appears that I needed to take stuff off of the glass.
Once stripped, I observed the water beading cleanly. I'll hold off on the claybar for now, as it seems unnecessary. I also "abraded" the blades themselves with the cleanser. I'm afraid they are gunked by the Prestone though, as they actually feel tacky and will still chatter a tad, on and off, though their passage over the glass surface is hugely improved.
One downside. Overall, the clean glass is a good thing. But it does reveal how badly micro-pitted my winshield is after 14 months in New Orleans. Maybe one of the benefits of the Rain-X is a "waxing" effect that helps partially conceal all the little pits. Still, overall, I'm very pleased with the cleanliness. Now I'll need a good heavy rainstorm to determine whether I can do without the RX.