Wow, those are awesome! I've never seen anything like that in a residence. It must have been heartbreaking to see the damage. I'm glad you got good replacements.
The last photo looks like etched work to me, judging by the crisp outline with just a bit eaten away outside the outline. That could happen with etched work, while the directional spray of abrasives would be less likely to stray beyond the edges of the resist.
I'm not sure I'd call them Nouveau, though there's certainly overlap between Victorian and Nouveau styles. If they were Nouveau I would expect more naturalistic intertwining vines and asymmetry. That's just my take on it, though.
...(edit, after seeing Frank's latest post) Polishing those babies uniformly without going outside the lines would be a challenge! Maybe with tape over the colored parts you could do it, but then there's the added challenge of cutting the tape to match exactly the areas to be polished. I don't know if it's worth the time and effort involved, unless you're ready for a LOT of Zen evenings!
...(and another edit, after seeing your post) Maybe with a Dremel, using emory-impregnated tips?