The use of spreadsheets is widespread. Be it in business, finance, engineering or other areas, spreadsheets are created for their flexibility and ease to quickly model a problem. Very often they evolve from simple prototypes to implementations of crucial business logic. Spreadsheets that play a crucial role in an organization will naturally have a long lifespan and will be maintained and evolved by several people. Therefore, it is important not only to look at their reliability, i.e., how well is the intended functionality implemented, but also at their maintainability, i.e., how easy it is to diagnose a spreadsheet for deficiencies and modify it without degrading its quality. In this position paper we argue for the need to create a model to estimate the maintainability of a spreadsheet based on (automated) measurement. We propose to do so by applying a structured methodology that has already shown its value in the estimation of maintainability of software products. We also argue for the creation of a curated, community-contributed repository of spreadsheets.