Yes - Plymouth to Saltash and Liskeard
A little bit of an exception to the "gone or improved" rule ... just look at the inbound series of trains to stations such as Dockyard in the early morning, and the afternoon flow back out ... and look at the very thin service if you're making a journey such as Devonport to Saltash we have today compared to this. Menheniot hasn't fared too well, either.
While "the Beach" from Bristol has thrived, the local service from Plymouth appears to have withered. Would / could there have been a case to have done better in Devon on this one? Indeed - would there be potential to this day?
"the beach" might be thriving in relative terms now, but it was a long old haul to get there. Closure from Stapleton Road through to Severn Beach had actually been announced in February 1967 just before grahame's timetable came into effect, and was only reversed in July 1967 after an enquiry.
It would be fair to say that it struggled through the next 3 decades, before the 1990's saw the bustitution of all daytime trains between Avonmouth and Severn Beach. Two further closure proposals were then fought off, in 2004 (Clifton Down-Severn Beach) and 2007 (Avonmouth-Severn Beach and Pilning), before all the years of
FoSBR» -led hard work and lobbying finally paid off in 2008 when a vastly-improved service to Avonmouth with all-day, all-rail extensions through to Severn Beach was introduced.
As far as Devonport, Dockyard, Keyham and St Budeaux Victoria Road go, it appears to be the case that once the line through to Tavistock and Okehampton had gone, and the decision to retain Gunnislake had been taken, they simply became regarded as "branch line halts" on that route, with a handful of peak mainline calls thrown in, a status made all the more obvious with the decimation of the number of services calling at the main line only St Budeaux Ferry Road. This has more or less remained a constant over the intervening years, rather than services having particularly "withered" over time.
I personally am a great believer in the potential of frequent Plymouth urban rail services, and to be fair to the admirably pro-rail Plymouth City Council, they have put forward a number of very good Plymouth Metro-style proposals over the years. It's just a great shame they havent received a fairer hearing from the powers that be.
