The character of Crazy Sue Dunham on page 229 is real, and lifted straight from the pages of The Berkshire Hills. She is also described in 'The Secret Integration'.
As for the Specter, it is described on page 42 of The Berkshire Hills:
'Of the stories and legends about Old Greylock, the one about the 'Specter' is most popular ... The phenomenon of a gigantic shadow of an object reflected in a cloud is so well known as to have a German name, Brockengespenst (Specter of the Brocken) from Brocken, the highest peak of the Hartz Mountains. As Greylockgespenst would be a bit unwieldy for Berkshire, here it is simply called the Specter.'