Ya know, an easy way to validate the Smilers presence throughout the ship (other than just as an obvious creepy government-is-watching-you image) would have been for them to act as guides and info kiosks. The Doctor could run up to one and tap on the glass, ask it for directions or something and have it answer in turn, then later have the little girl explain that no one uses them for that anymore in a spooky ominous kind of way.
Their purpose was demonstrated in the very opening scene of the show. They were teachers and offered warnings (by changing their face) when people were doing things they weren't supposed to be doing. They weren't aggressive or intentionally "evil" or anything; just an automated work force responsible for law enforcement, education, and probably other similar civil duties. The Winders, on the other hand, were there to keep things running and act as backup when the Smilers weren't able to perform their duty.
At least that's what I got from it. People only feared them because they
were impartial disciplinarians, and they knew people disappeared from time to time. Which wasn't a function of the Smilers so much as the Queen and the Winders behind the scenes.