Although the Kent Coast electrification seemed to be done for longer distance flows - most obviously Dover and Thanet <-> London - this certainly didn't seem to be where most of the passengers were travelling by the 1980s. A significant cohort of long-distance super-commuters from places like Herne Bay who had moved out there around 1960 with a view to later seaside retirement had indeed retired. The days of trains being able to run full non-stop from Whitstable to Cannon Street had long gone.
In contrast a vast number of houses had been built around the Medway towns, largely driven by the construction of the M2. Journeys to the Medway were under an hour and the demand for refreshments was far less. Rising demand dictated 12-VEP formations on the busiest trains with no scope for a buffet.
Slightly off-topic, but in about 1993 Network SouthEast introduced a blanket smoking ban on all NSE trains with the exception of longer-distance South Western Division services. I remember seeing posters at stations on the South Eastern Division announcing the forthcoming smoking ban saying that the average journey time on Kent Coast services was only 40 minutes, and because of this NSE considered it reasonable to ban smoking.
I guess this reflected the fact (as Dr Hoo alluded to in entry 18 above) that by the 1980s and 90s most passengers on longer-distance SED trains were travelling intermediately (e.g. London-Medway towns, Medway towns-Faversham, Faversham-Dover/Thanet) rather than end to end. This may well also be the reason that Charing Cross-Dover-Ramsgate trains no longer ran non-stop between Waterloo East and Ashford from about 1989 onwards: presumably by this time not many people were travelling all the way from London to the likes of Ashford, Folkestone, Dover, Deal and Sandwich, so BR probably deemed that the inconvenience caused to such passengers by making their journeys a few minutes longer would be outweighed by adding stops at stations such as Orpington, Sevenoaks and Tonbridge that would generate extra traffic (and extra revenue) for these trains.
The Central Division's catering provision always seemed somewhat over-generous - Pullmans with full meal services surviving into the seventies, on a route with a journey time of an hour, seems incredible now. Possibly just a historical accident, given that the LBSCR was a keen user of Pullman cars.
Just noticed an item in the October 1980 Railway Magazine. The last five Hastings buffet cars were due to cease 'in May' but had a stay of execution until 22 August whist a commuter group 'Save Our Buffets' (SOB) worked with BR to try and find commercial/advertising sponsorship.
In the January 1980 edition there was a report on a (national) review of train catering in which 'only' Clacton, Ramsgate and Hastings were to be chopped, from May. Withdrawal of the Ramsgate services (presumably meaning the BEPs) would allow catering services on the Dover route to be 'stepped up' in connection with Seaspeed hovercraft services.
So it looks as though Dover was definitely given a 'last chance' around 1980-81.
Again slightly off-topic as Clacton is Eastern Region, but I think you could also say that the griddle car service on the Clacton line in the 1960s and '70s, for the first 20 or so years of the Class 309 EMUs, was rather over-generous for a route with an end to end journey time of only about 90 minutes. A griddle car wasn't the same as a full restaurant car service, but even so it would seem incredible now for a journey of that sort of length. And as with the Kent coast resorts such as Margate and Ramsgate, I would guess that Clacton would be the sort of place that could attract large numbers of visitors on a fine summer day but probably didn't enjoy anywhere near as much year-round traffic as places like Brighton or Bournemouth.
I'm guessing that when the CEP refurbishments started, BR hoped that the hovercraft and jetfoil services from Dover would help to boost takings on South Eastern Division buffet cars on both boat trains and normal services, so they kept them on Dover services for a while after their withdrawal from the Victoria-Chatham-Ramsgate route on a use-it-or-lose-it basis, but in the event it wasn't the success that had been anticipated so they decided to do away with all on-train catering on the SED, thereby reducing the cost of the CEP refurbishment programme by converting most of the BEPs to CEPs.