I play double bass, and in Chuck Traeger's book on bass repair, he is pretty blunt: "You get paid to be heard." Loudness is definitely a quality factor with a direct influence on price.

Instruments with a sweet tone quality, but lacking in volume, are a tough sell, and will often be modified to bring out more sound. With the exception of a few museum pieces, the Strads have all been modified over the years to make them louder, with longer necks and shorter ribs.

I suspect the cello edged out the viola da gamba because of volume.