"Places that didn't get visted by too many enthusiasts"?
Not really, by the time I started they were roughly divided 2/3 on the Eastern, which is my stamping ground, and 13 on the Western.
I joined the Dalescroft railfans society, and undertook a saturation trip to S.Wales with them to knock off most of the Western ones, plus those at Bath Road.
The eastern ones were done, as you say, on rail-borne outings with the odd trip out by car. Once I'd done Stratford, Colchester, Ipswich, march, Kings Lynn, Lincoln, Hull, Darlington, and Newcastle, that was pretty much it. There were a few in W.Yorkshire, around Bradford, Halifax etc, but I got those mostly by car.
Oddments were done by Rail: two at Bournemouth, three at derby, and quite a few via the Plant.