Cost-Benefit Analysis of the 64.6 Billion Yen Sendai New Music Hall Project: A Comparative Examination with the 2013 "3.0 Billion Yen, 1,500 Seats" Academic Model and AI-Driven Validation

【Executive Summary】 As the construction costs for the Sendai New Music Hall in Miyagi Prefecture have surged to an unprecedented 64.6 billion JPY, this study re-evaluates the validity of this investment against the "3.0 billion JPY / 1,500 seats" benchmark established in a 2013 academic paper. By integrating a standardized Social Cost-Benefit Analysis (CBA) based on Ministry of Internal Affairs and Communications (MIC) guidelines—executed through Google NotebookLM for exhaustive simulation—this report demonstrates that both the 2013 theoretical model and the 2026 empirical data independently converge on the same "Safe Zone" of 3.0 billion JPY. This finding suggests that the current 64.6 billion JPY plan represents a significant "overshoot" that exceeds academic and economic rationality. 【Abstract】 This article evaluates the fiscal and social sustainability of the Sendai New Music Hall project. It contrasts the current 64.6 billion JPY budget with the "3 billion JPY/1,500 seats" threshold proposed by Keiichi Shigano (2013). Utilizing the Regional Economy Analysis System (RESAS) and standardized CBA methodology, the author conducted an exhaustive round-robin calculation of variables. The results confirm that net social benefit (W) is only maximized within the 3.0–5.0 billion JPY range, effectively debunking claims that current cost increases are merely due to unavoidable inflation.