I have a B/W Philco with a 21" CRT that's also very slow to wake up. It tests low on emission, but with a brightener it's watchable (not perfect, but watchable) after a few minutes.
I have been debating whether to try the CR70's restore function on that one. I tried it one other time on a weak 17" tube, which helped somewhat but wasn't a miracle cure. Perhaps that would be wiser than running it on a brightener until it completely croaks . . . .
Re painting the cabinet black, I don't think that would be awful. I have a CTC-11 with enameled black cabinet and it looks fine (better than faux wood, which I don't like). When I started work on my CTC-7, I was surprised to see that RCA sold that chassis under 46 different model numbers. Who knows, maybe one of those cabinet options was black
Regards,
Phil Nelson