The reduction in the price target by a reputable analyst like Steven Alexopoulos from JP Morgan could lead to a negative short-term sentiment among investors, potentially causing a decrease in the stock price of Valley National Bancorp. The maintenance of a Neutral rating indicates that the analyst does not see significant upside or downside from the current price level, but the lowering of the price target suggests a reassessment of the stock's value potential, which could influence investor perception and stock performance in the short term.