I think I may have found a cause for the especially noticeable degradation of the siding on the bedroom wing at Wingspread, seen in the first photo above and in the trailer.
If the foliage of a tree formerly located near that wall had been in contact with the siding for an extended period, one could expect moisture trapped there after every rain or snow-fall to accelerate the weathering of that siding.
Choosing "masterpieces" from Wright's catalog is one means of settling on a selection for inspection and praise. The volume titled "Frank Lloyd Wright -- The Masterworks" (Pfeiffer; Rizzoli, 1993 -- a banner year for Wright publications) contains 39 buildings. Do all of them represent the best of Wright's work ? Perhaps -- but the selection is surely subjective. Perhaps a more limited grouping, such as we have in the forthcoming movie, will be more persuasive as a quasi-definitive list of "masterpieces" ?
One suspects that the selection process may have as much to do with availability -- of good photographs of buildings in good condition, in the case of the book -- as with a persuasive argument that a given group of subjects can be defended as definitive masterworks . . .
SDR