A few years ago I was part of a group on a 'guided tour' of BA at Heathrow. Of the various briefings that stick in my mind one appropriate to this topic must be 'Cabins are maintained to a standard such that a passenger entering an aircraft should not know whether they are in the oldest or newest aircraft in the fleet'.
I know you can take that two ways, (one of us did and had to buy the drinks at lunch
) but I think generally they maintain the expected high standard, even on the 'old' 737s which are now my chariot of choice. And thanks to the crews too, not only for the champagne.
(Now can I have my upgrade .... please?)