During the early pre-Barnabas eps of DS, whenever Josette's ghost appeared it was accompanied by the scent of Jasmine. However, when we went back in time and actually met Josette, there was no mention of her love for Jasmine. (Just Rose Water.) Likewise, with the ghost of Daphne it was the scent of lilacs, yet in 1840 when she is alive there is no mention of her liking lilacs or the scent of them.
Paranormal experts often report that the appearance of a benevolent spirit is accompanied by a pleasant smell. The scent of flowers may be indicative of a friendly ghost rather than that ghost's preference of perfumes while they were alive.
By the same token, it is often said that the presense of an evil spirit is accompanied by a foul smell. There is no indication that Quentin or Gerard ever left an unfortunate odor so they might have chosen to simply ignore this aspect. It would be funny, though, to see David and Amy holding their noses upon exiting the West Wing.