While the SPDR S&P 500 ETF Trust (SPY) is not directly affected by the Federal Reserve's specific policies on agency debt and mortgage-backed securities, its value is influenced by overall market sentiment and the monetary policy environment. The Fed's decision to maintain the runoff cap could be interpreted by investors as a sign of its stance on monetary policy stability, which in turn could affect investor confidence and market movements. However, the indirect nature of this impact and the broad range of factors influencing SPY's value lead to a neutral score with moderate relevance and importance.