I am led to believe that it is inadvisable to drop the top in frosty conditions as the plastic can crack. Also, the glass window has a de-mister whereas the plastic hasn't and the plastic will become opaque over time. The 2004 models with the glass window also have the stiffer monocoque and updated software although that can, apparently, be updated.
New a chap in Chepstow many moons ago that had a 2 tone Bi Turbo Spyder...He dropped the roof on a frosty day and the rear screen cracked so could well believe that Benny.