Over the long-term, you want to grow the number of your above-average customers so they make up a larger part of your customer base.
You should absolutely continue to grow your customer base as a whole through customer acquisition. You just want to accumulate more above-average customers as you go.
There is no best number of above-average customers. What is best for one store might not apply to another.
Ideally you want it high and to be growing over-time. A good segmenting system like Repeat Customer Insights should keep track of it month by month for you.
Eric Davis
Analyze your customer's behaviors before they defect
Your customers aren't yours forever. Some might have defected today, never to be seen again.
You need to analyze your customer behavior so you can reach them before they defect.