It's a simple idea. People in SD get dirty, why not rooms? My idea is twofold: add a small cleanliness descriptor to every room (%L is dirty or %L is immaculate) and add a 'clean' command so people can tidy up. Rooms would get dirty over time, depending on what sector they're in and how heavily used they are. There would have to be maximum and minimum cleanliness levels (Blue is always immaculate, the sewers are always nightmarishly filthy) and the cleanliness of a room would determine how dirty a character gets walking through it.
WHY WE NEED IT
Unlike most ideas on the BGBB, this change would affect EVERYONE. It would make the game more realistic and provide more interesting jobs to a growing player base. Corpie wannabes could start out at their chosen soul suckers as a simple caretaker, and imagine the plot one could get into cleaning up the CEO's office. Bars could hire cleaning staff that actually affect the world codedly, and WCS would have more to do than just corpse removal. Cabbies would have to keep their rides proper, and everyone could marvel at how Blue keeps its streets so tidy.
Bottom line: even if it would be a bitch to code, this addition would be greatly beneficial to the game as a whole, on nearly all fronts. I highly encourage its installment.