To The Editor: My first nightmare occurred right after recent news that the three white bungalows along Rt. 1 at Longwood were doomed to demolition.  Those houses were built in the 1920s by P. S. du Pont for some of his closest employees.  Rather I saw in their stead a grand entrance with blinking marquee, announcing a Broadway show or band  at the new indoor theater, constructed on the once grassy...