Convergent Socio-Economic Analysis of the 64.6 Billion Yen Sendai Music Hall Project: Evaluating Sustainable Investment Ceilings through CBA and Primary Field Data on Infrastructure Redundancy

The municipal government of Sendai is advancing a 64.6 billion yen project for a 2,000-seat "Music Hall and Disaster Memorial Complex." This study conducts a rigorous socio-economic feasibility assessment by integrating a 567-pattern exhaustive Cost-Benefit Analysis (CBA) with primary field survey data. By fixing the evaluation period to 24 years (2026–2050)—the reliability limit of RESAS population projections—the simulation independently converges on the "3.0 billion yen, 1,500-seat" model established in 2013 as the only sustainable investment range. Furthermore, empirical field audits revealed that competing infrastructure within a 5-minute radius, specifically Tohoku University’s Kawauchi Hagi Hall, suffers from significant underutilization; primary evidence shows that even its "home" organizations, such as the Tohoku University Mixed Chorus, bypass the facility in favor of other municipal venues. The current 64.6-billion-yen plan represents a 20-fold deviation from academic benchmarks, posing a severe fiscal risk to future generations in a shrinking society.