Resumen: In advanced economies characterized by sustained immigration, rising inequality, and chronically underdeveloped social housing sectors, demand-side welfare interventions risk being capitalized into higher rents rather than improving housing affordability. This study investigates how Spain’s welfare state transformation—particularly the rollout of IPREM-indexed policies such as the Minimum Living Income (IMV) and the Youth Rental Voucher—interacted with migration flows and tourism-driven housing competition to reshape private rental markets between 2008 and 2025. Using harmonized national data from OPI, Idealista, INE, and the Bank of Spain (2010–2024), we apply a descriptive time-series approach that combines structural break tests (Chow and Bai–Perron), pre/post-2021 correlation comparisons, regional heterogeneity analysis, and robustness checks (including Spearman correlations and jackknife sensitivity analyses). We identify a pronounced structural break in 2021: while consular visa issuances—a proxy for combined migration and tourism inflows—showed no significant association with advertised rental prices before 2021 (r ≈ 0.27, p = 0.41), a remarkably strong co-movement emerged thereafter (r ≈ 0.90–0.92). This shift aligns precisely with the nationwide implementation of IMV, institutionalization of the Youth Voucher, and disbursement of EU Recovery and Resilience Facility funds. The effect is most acute in regions with rigid housing supply and high exposure to tourist-use dwellings (VUT)—notably the Balearic Islands, Murcia, Cantabria, and Navarre—suggesting that increased effective demand may have been absorbed primarily through price increases rather than expanded access. While our observational design precludes causal inference and the findings should be interpreted as exploratory and hypothesis-generating, the convergence of timing, magnitude, and institutional context renders a policy-mediated demand channel plausible. The results caution that, without complementary supply-side measures—such as social housing investment, rehabilitation incentives, or VUT regulation—demand-side subsidies may inadvertently reinforce housing inequality and reduce fiscal efficiency, thereby undermining the sustainability goals they aim to advance. Idioma: Inglés DOI: 10.3390/su172310617 Año: 2025 Publicado en: Sustainability (Switzerland) 17, 23 (2025), 10617 [26 pp.] ISSN: 2071-1050 Tipo y forma: Artículo (Versión definitiva) Área (Departamento): Área Geografía Humana (Dpto. Geograf. Ordenac.Territ.)