A Tale of Two Cities...
Exeter (popn. about 110,000) has a very convenient Central station, a surprisingly high number of other stations within the city boundary and a radial network of local lines. The Devon Metro is doing very well - Exmouth has the best ever service in its history, Barnstaple trains are wedged, Okehampton is a success and the Riviera Line is booming. Hopefully local trains from Taunton serving Wellington and Cullompton and a local service to Cranbrook and Axminster will soon be added. But it wasn't always like this - Exmouth was slated for closure by Beeching; Barnstaple and Okehampton were not but Okehampton went anyway and Barnstaple was seriously threatened when the bridges at Cowley Bridge needed replacing. By the '70s the Riviera Line local service was very thin and stations like Starcross and St.Thomas had little more than a token service.
Plymouth (popn. about 250,000),however, has an inconvenient main station and low local usage with just the main-line into Cornwall and the Gunnislake service. Such local lines as there were went before Beeching (Turnchapel, Yealmpton, Tavistock G.W.R) whilst Tavistock S.R. went with Beeching. The planners in their wisdom after the destruction of WW2 dispersed housing, the main hospital and employment centres to the north of the city where there was never a railway anyway. So it is very much a car centric city - with equally chronic congestion as Exeter - and the city council is still stuck in '60s/'70s 'just one more lane' mode. The major Manadon Interchange (A38 / A386) is to be rebuilt. but it will quickly fill up and solve nothing.
So Plymouth is a tougher nut to crack for rail travel - reopening to Tavistock and a station at Plympton would be a start. The city would be ideal for a tram or tram/train system in my view - it has wide European style boulevards in the city centre and could penetrate areas that rail cannot. Plymouth's twin in Brittany, Brest, with a similar population has a successful system and has just opened a second line. In the U.K., however, trams give politicians the vapours - and certain posters on here too!