I have been working with Spencer opals for the past two years and can not seem to find much information about them.
Downing, in his book about the Appraisal of Opals states that Spencer Opal triplets are generally more valuable than triplets from other locales. However, that is the only fact I know about the value of Spencer’s.
Spencer Opals from Idaho occur in multiple, thin layers of color and are much more difficult to work with than any other variety.
Personally ,I would rather work with any other variety, since they are not as tempermental as Spencer.