Families of products are steadily emerging for distinct settings such as embedded systems, navigational systems, financial applications or even web applications. This shifts the attention from individual product-centric development to software product line development where the focus is on constructing reusable assets from which customerspecific products are obtained. This paper tackles the maintenance of an entire family of products, describing our approach to quantifying maintainability. We report our experience measuring the maintainability index of each product in the family, and then propose a generalization of the results in terms of the entire family or product line. This exposes a number of benefits towards the improvement of product-line maintainability, enhancing ultimately customer-specific products.