Alright @crinrict I wasn't sure if it would be same issue or not, but it does sound related now that I'm more awake.
I did some travelling to other houses (all original from the game that I have never touched), which are all about equally sparsely decorated. In some my travelling sims have no complaints, in others they immediately complain about "poor" or "dismal" decoration as soon as they step onto the lot, and just looking at these houses I cannot see any significant difference in the decor at all. With my superstar actress she will come home from a gig (or someplace else) and as soon as she steps onto the lot it goes "poorly decorated", and that's despite having to walk several tiles from the lot edge to get to her house.
To me it looks like (but it's difficult to say for sure) anything with 0 bonus environment gets counted as a harsh negative penalty, while none of the stuff with bonus environment does anything significant for the score at all. Either way it should not be possible to reach a negative decor score when there's nothing to detract from the decor (like trash and unpainted walls).
