“How many displays are enough in any given venue, and when is it too much?”
I don’t think that there is any special number of displays that is the right number or not enough. It’s more what the experience requires, how you want to impact the space, what your budget is. As with any experience, you don’t want to overstimulate the customer you are trying to attract, but I’d say most of the time that is done with the content and not an issue based on the number of displays used. It’s important to remember to evaluate the space, the experience you’re trying to create, and the impact your solution has on the customer.