My first game was going horribly, so when my husband got the bonus throne rooms I started a new game with the Princess castle, and whoa! All of the rooms are much more lavish, with higher end furnishings, and wall coverings. I got rid of the Disney Princess colours, and redid it in royal purple and gold. The well decorated buff was present without my having to buy or upgrade anything.
My bard was getting robbed so much that, whenever she has a large amount of money, I buy her gorgeous paintings, and furniture for her room. So my castle and the room over the tavern are the two most stunning places in my kingdom. I've actually spent more on the tavern room, as the castle was already well decorated.