Do higher levels of party system institutionalization make party mobilization more inclusive, or do they primarily intensify outreach to citizens who are already politically engaged? Prevailing theories of party development assume that organizational consolidation lowers mobilization costs and broadens political inclusion. Yet existing research has focused largely on whether institutionalized party systems mobilize more, rather than on whether institutionalization reshapes who is mobilised. This article advances a capacity-based account of party system institutionalization that distinguishes between the scale and social distribution of mobilization. Using individual-level data on party-initiated campaign contact from Afrobarometer Round 8, combined with system-level measures of institutionalization from the Varieties of Democracy project across 33 African countries, the analysis examines how organisational capacity shapes patterns of party outreach. The results show that higher levels of party system institutionalisation are associated with higher party contact. However, these increases do not translate into more inclusive mobilisation. Politically embedded citizens' partisan identifiers, prior voters, and civically engaged individuals remain significantly more likely to be contacted as mobilization expands with rising organizational capacity. By distinguishing between mobilization volume and mobilization distribution, the article reframes party system institutionalization as a capacity-enhancing rather than redistributive mechanism and highlights the limits of organizational consolidation for inclusive mobilization.