No of course I wouldn't ask for coffee at such a time! 15 minutes before top-of-drop is hardly unreasonable though.
It was a BA pursar who tipped me off about the 'early coffee' trick. He regularly has to stop his team trying to do it and tells them to wait until the passengers are on their dessert course. Early coffee = finished early = cleared away early = more time for his 'girls' (as he calls them) to relax (he's long haul) - I hope he was just joking...... But more seriously, if the airline can get away with less cabin service then they'll be able to reduce crewing levels to the minimum required under JAR-OPS - that'll please the bean counters until the passengers vote with their feet.
Write letters? Certainly! And fill out the in-flight surveys giving high marks for the cabin crews' standard and low marks for the airline's service. They used to be able to provide such levels of service on a 1:20 flight - and that included a 3 course hot meal, not just the current 2 course cold snack!