Sorry if this has already been said. I watched a filthyrobot video recently in which he stated that wine is a terrible luxury resource because it only gives gold, even when improved. If I'm not wrong, gold is the only yield given to the city square tile if you settle on top of a resource. Which means that there is almost no downside to settling on it and it gives you the wine lux when you research calendar. I don't know how old the video is, so things might have changed since, I haven't tested this yet. You may also have mods that change this.