We have found tours to be helpful and are trying to keep growing that aspect of our business. I don't think I would want to make that the main focus of our sales as its not always easy to keep growing the number of tour takers.
I dont have any solid numbers on how much our tour visitors spend but here are a few observations.
Small parties of two or four that come to your location because they have heard of you and are excited to visit, or they are regular craft brewery/craft distillery visitors, or foodies in general will buy bottles. (perhaps one bottle sold per 3 visitors) They have multiple drinks and leave with bottles. Anyone who drives to your distillery on their own will be the best visitors/tour takers.
Bachelor party type tours, or group tours that arrive in a limo, mini-buss, etc. (typically 10-15 people) will all get at least one drink at the bar. If they have other locations to visit as part of their tour then they are done after that first drink. You might sell one bottle to the one person in that group who randomly likes to make cocktails at home.
30-45 person bus group tours filled with an older crowd will take the tour, not drink, and not buy bottles. The last bus group tour I gave I sold exactly one $15 t-shirt.