I've enjoyed this thread immensely, because so little is known about the 19th-century Saxon RF besides the scandal surrounding Crown Princess Luise, because they neither were part of the Queen Victoria/Glücksborg clan nor produced such celebrities as the Habsburgs and Wittelsbachs.
The dynasty was increasingly unpopular in the nineteenth century. The Catholicism of the ruling house (the people were mostly protestants) may have been a factor.
Did this perhaps lead to them surrounding themselves with more exclusive, old, imperial nobility, which often was Catholic, instead of possibly more liberal Protestant "meritocrats" ennobled through state service?
I guess also the fact that Saxony was the second most heavily industrialized area in the German Empire (after Prussia's Ruhr Area) and thus the cradle of a very strong Socialist movement (of course very much celebrated in the GDR (DDR)) also led to increasing alienation between RF and subjects. Plus that instead of increasing the franchise, like the liberal medium-sized German states, they went reactionary and adopted the Prussian model.
The personal union with Poland was never a success. The partners were too different. The Wettiner persisted in this dream however, even after Poland had ceased to exist. It was one of the reasons Frederick Augustus I supported Napoleon, which led to an embarassing and bloody defeat at the Battle of Leipzig in 1813, followed by the loss of half of Saxony's territory.
This is so shocking in the age when the other main dynasties increased their territory so much through secularisation and mediasation!
I also guess that the fact that the elevation of the old electorate to a kingdom was mired with that huge defeat also can explain why the Saxon RF with their treasure trove of jewels in the Green Vault, never bothered to acquire new royal regalia (besides the old Polish ones they already possessed) like the other new-minted sovereigns of Bavaria, Württemberg, Baden (and later, when they no longer were in personal union with the UK, also) Hanover.
If Saxony was not to be destroyed (saved only by Metternich), do you think it would have received the lands of the Ernestine branch and the other Thuringian duchies and principalities as mediatized territories?
Is anything known about how this loss affected the Saxon RF in the long run, for example their attitude towards Prussia? I can't believe they risked it all once more by supporting Austria in 1866!