Re: Legibility of 'Decorative' Typefaces - 'A' yet again . . .

As you point out, the A sets next to the B which looks much heavier... If you strip away the serifs and shading, the base of the A is 23 units wide. The B is 28 units wide. I don't think the issue is that the A is too narrow, rather that the other letters are all too wide.
Looking at the photos in Todd Hackett's post, nos 1, 88 and 109 all have a tall, slim font, and the A at its base is (as far as I can tell holding a rule against the screen) the same width as the R that precedes it. The "Worlds Fair" font, no 169 is a "fat as it is tall" font. The R has no serif at lower right. Above serif level, the A is approx 2 pts wider than the R, which only achieves full width at the absolute lowest point.
Your Sonoma font, which I think looks very well btw, the A is approximately 33% wider than any other letter, but this gives it enough "weight" to stand amongst the other letters. The M is unusually narrow for a capital M, possibly looking a little cramped in the crotch, but as there is no M in "North Pacific Coast", and the name Sonoma is painted in the roman style very like Eureka it is hard to know. If only someone had promoted a "Middle Pacific Coast" narrow gauge road, it might matter