Haven't heard about the extra cost for the paint. It's a pretty common color, but there are other sources that show the percentage at around 6% of production. 6% of 600,000 cars is 36,000. If it were 10%, it would be 60,000 cars. I wouldn't consider that limited production.
Would be interesting to see documentation regarding extra cost for the paint. I bet it was tough for them to match the panels, just like all the other metallic paints. I know that whenever I have seen an original paint emberglow car, the paint is usually dried out on the top surfaces. From what I understand, the size and type of metallic added to the paint back then would hold heat longer and the surface would get hotter.