I ate at a wonderful South Indian restaurant recently. It was lunch,
the restaurant was nearly empty but the music was loud and had little
connection to India....more like German techno. I asked the servers
about the music and they all said the music was driving them nuts. I
talked to the two managers who were there and one owner. They said it
was due to the other owner who loved making the play list for the music.
This is a white tablecloth high end, high quality restaurant. In general I would say music is barely appropriate; maybe softly, maybe in the evening to get the young crowd talking louder, but barely. I know many flash in the pan hot hot hot restaurants have plenty of music and have it loud. Flash-in-the-pan is the operative term.
My business experience is that such restaurants can't last very long for three reasons. (1) Any specific form of music always appeals to a specific market; you are not likely to get customers outside that market. (2) The hot hot hot restaurant can't expect to be hot for long and the music will have offended or discouraged the other markets that might have come in after the hot-hot has died down. (3) One hell of a lot of paying diners avoid loud music and many avoid any kind of music they don't like.
I think music is a very limited and dangerous business draw.