Why on earth would you think fares would come down overall if Advance tickets were abolished? The exact opposite would happen and fares would increase substantially.
Advance fares attract voluntary travellers, and if those substantially cheaper fares were removed and the only option was the full price ticket then quite simply a proportion of these people would not travel. So now you are taking less revenue and your full price fares go up, so even more of these travellers stop travelling (and some of your full price travellers). And so on, and so on.
Anyway, back to the issue, it seems to me the usual rail industry foul up.
Everyone saying one member of staff should or should not have done something, and meanwhile the poor customer who is only following the guidance they were given, is the one who suffers.
Agree with that, and if you also add on the spend at larger stations which have a decent retail offer, then the effect would be noticeable. Im not so sure I agree with your " usual rail industry foul up " comment though.