Urban leftover spaces, excluded from the urban fabric’s structural integrity, may become socio-spatial focal points of decline due to their functional and semantic ambiguities. This study examines how these underutilized spaces can be reimagined as potential areas by identifying the problems and needs of their users in the Osmanağa, Caferağa and Rasimpaşa neighborhoods of Kadıköy, which are characterized by excessive and irregular user density and are in a state of constant change. The primary focus of the research is on participatory planning approaches that elevate the user to the status of co-designer in urban interventions. Methodologically, the study involved an analysis of qualitative data sets relating to the participatory planning activities of the Istanbul Metropolitan Municipality (IMM) for the period 2020–2025. Qualitative data from the IMM’s participatory planning reports were examined through thematic classification and interpretive spatial visualization to identify physical, social, and administrative problems and potentials in the selected neighborhoods. The findings indicate that commercial pressure, sidewalk occupation, interrupted pedestrian access, insufficient public facilities, and unplanned development may contribute to spatial neglect. When these conditions persist, they may increase the potential for the formation of leftover spaces. By relating the reported problems and recommendations to their approximate spatial references, the study provides a context-specific framework for interpreting conditions associated with spatial neglect and considering possible public-space interventions.