Seth's post offer some kindle to this discussion;
Write it down. Post it on the wall. What would happen if you spent 100% of that amount on each of your next ten new customers? That's more money than you have to spend right now, I know that, but what would happen? Imagine how fast you would grow, how quickly the word would spread.
Imagine if your staff embraced customers as lifetime partners in the business. Actively tried to build a book of business by their service and in doing so grew the restaurant. Imagine that every customer is not a single transaction, but a continual stream of transactions. How do you treat that customer? Why are you not doing that to every customer that walks in the door? This is a cultural discussion, your establishment either treats all their customers as a relationship or it does not.
It is pretty obvious which establishments value the lifetime customer!