One of the fundamentals of business is that it's always easier and cheaper to sell more to your existing customers than it is to go out and find new customers. A little extra effort to make a repeat customer happy is sure to pay off. Think about how many people he has told about your place over the years.
You have the perfect opportunity, and I think you have said you do this, to find out where your customers found out about your place. I bet word of mouth would draw in far more people than any paid advertising you could do.