I would recommend Gordon Fisher with an online version of Marriage of Divorce of Astronomy and Astrology: A History of Astral Prediction from Antiquity to Newton which has a chapter on John Dee and Astrological Physics (chapter 10, the chapter doesnt appear on the table of contents, its somewhat of a hidden chapter, go to chapter 9 and access chapter 10 from there).
Then there is the article Jugglers or Scholars? negotiating the role of a mathematical practitioner by Katherine Hill in BJHS [PDF, 194 KB] which offers some perspective on the status of mathematicians and mathematics in the time of John Dee.
Less interesting, there is also the article Madoc and John Dee: Welsh Myth and Elizabethan Imperialism in the Elizabethan Review.
And related to Dee and mathematics in his time is also Darke Starre: Thomas Digges Perfit Description of The Celestiall Orbes at Dartmouth