With world enough and time, you might visit "Angels and Ministers of Grace: Theatrical Superstitions through the Ages" by Krsitin McDermott.
It places superstitions about productions of Macbeth in a larger theatrical context. Make of its slightly mystical conclusion what you will.
For those of you intersted in the historical Richard, the Richard III Society is devoted to a reassessment of him as a historical figure, rather than a figure of legend, propaganda, and sheer dramatic villainy..