Hello Jeff:
Yes, Rieseberg wrote about the Santa Cruz, as did Potter. In Potter's book (1972) he noted: Besides Rieseberg's report, "Other reports from England place the ship's location twenty-five miles farther north in Cardigan Bay, and describe her cargo as being 220 chests of gold and 2 1/2 tons of silver worth $2,500,000."
The silver alone would be worth $1M today (assuming 92% pure and $13.25/oz.), and further assuming such a vessel existed and sank with that cargo.
Don..