I'm going to have to disagree with you unfortunately. I much prefer my sims NOT being happy just because a room is well decorated.
For me, it just doesn't make sense. If I'm depressed, if I walk into a well decorated room, I don't immediately become happy. That's not how human emotions work.
I'm not saying that the Sims has to be entirely realistic, but I'd like at least a little semblance to reality.
I'm thrilled that they toned down this moodlet. Finally my sims aren't happy all the time.
That's just my preference though.