Like television ads, I think areas with things that would warrant warnings or announcements, would benefit from some flavor sounds.
An example: You hear from the intercoms above "The 8:34 flight from NeoTrans to Freesky is departing in five minutes" followed by a calming dual note tone.
The Maglevs already have something similar to this in some locations, but I think that similar things would be fun flavor wise.
Another use of this would be something like you call 911 and report a fire in the area, the room has some kind of tone (depending on sector) that is like " A fire has been reported in this area. Please proceed to the closest evacuation point immediately. Help is on the way". Would add some flavor while you have to sit around in an area for things to occur.
Dunno, random overcaffinated thoughts of the day.