[Arran]

I've been somewhat focused on sets of the 1920s lately, and from what I've noted there was a sort of "Fad" with steel cabinet sets in the late 1920s, I'm not sure whom started it but almost every major manufacturer, and several mid rank manufacturers started turning them out from 1926 through 1930. For obvious reasons the steel cabinet models were a lot more durable then the wooden box models, so a lot of them have survived, the main thing that lets some down is this was also the same period when casting mechanical parts from pot metal became extremely popular. In part because of their rather generic appearance, and the pot metal issues, they are not as popular as the wooden "coffin" sets, which are also very common. If the set comes with the matching speaker this definitely helps things.
As far as I know the Philco 511 series sets did not use pot metal, or if they did it was in some place where it was not critical. On the other hand they also purportedly manufactured 67.000 of them, most in Spanish brown, so whilst you could conceivably conserve, and touch up the existing paint it is a lot of work to make it look right, and it won't make the set worth any more then just repainting it. It's hard to tell from photos but it also looks like the existing paint may have some adherence issues, where the paint is missing it looks like it scraped off rather easily.
Regards
Arran