I am not sure these would be considered unpublished benefits - but they are not well-advertised.

i) SE (and E) can access the domestic MLLs on arrival
ii) SEs can access the LHR arrival lounge, without having flown on AC (or without having flown at all)
iii) if you want to call the SE desk from abroad, whereby the "toll-free" number and access code do not exist, one can call the SE line collect. Most (but not all) the agents will accept the charges. I usually go through the Canada direct operator; many of whom seem to know of this privilege. The Canada direct operators are patient - if you remember, the SE line goes through a voice mail menu, and then there is a slight wait, before the agent will answer.
iv) sometimes, in business class, SEs will be approached first, about their meal selection.