In current research, the social return to citizens initiatives is important but often under-evaluated. Within this work, we collected the information that has emerged from measuring the social value of regenerative projects in shrinking cities. We used a case study of the regenerative project Gebrookerbos, a socio-spatial regeneration project in the shrinking city of Heerlen, the Netherlands. To assess the project’s monetary and immaterial aspects, a social cost–benefit analysis (SCBA) was used to understand the complexities of the costs and benefits associated with citizens in regeneration projects in a shrinking area. Drawing from the literature on urban shrinkage, citizen involvement, and social cost–benefit analyses, a theoretical framework was proposed. The case study included primary (i.e., interviews) and secondary (i.e., document analysis) data to identify the social value of the Gebrookerbos project, with results suggesting that the project has been meaningful to diverse stakeholders. Based on experiences with the SCBA of Gebrookerbos, one finding was the complexity of measuring citizens’ initiatives in terms of social return due to their process, organisation, and goals, in combination with the dynamics of shrinking cities. We discuss why research on social return to citizens’ initiatives is important and with this study we draw attention to the tendencies, opportunities, and future potential of citizens’ initiatives, which contribute to vacant open spaces and quality of life in shrinking cities.