What you've shown here goes hand-in-hand with a book that I read called "Return on Customer".
The author points out that most of us have a "new customer acquisition" mindset, but that this is often counter-productive. They go on to demonstrate that, at least in most cases, if we work toward realizing the potential of our existing customers, we'll see much more benefit.
The law of diminishing returns creeps in at some point, because each customer only has so much money. However, we should work toward maximizing the value that each customer brings to our shop.
The book has a lot of insightful points...many of which are over my head. I think I've gotten enough use out of it to cover the purchase price. B-)
