The common one is considered the 30s, though I've always thought that's a bit rose-tinted, perhaps, as the Bentleys, Bugattis, Delages, Talbot-Lagos, Lagondas and Rollers isn't really the fair cross-section of the working man's motoring life, which was a motorbike and sidecar, if that. Golden age for those that could afford it, perhaps, but that applies then, to anything. 'Golden age of Britain'-the early Victorian era - not if you're a slave or a chimneysweep. 'Golden age of France' - pre-revolutionary/republic France - not if you're someone starving to death and cholera-ridden while Versailles are vomiting with the vast amounts of food they're gorging themselves on etc etc...
I like your thoughs, with the 70s. Personally I like the 50s as an era, as a whole. Not only were the car designs fresh, but new, bold, American-influenced designs (as they were in the 70s of course) but The RAF was like a brand new Force with Jets, we had the finest car industry, aero industry, brand new nuclear powerplants, off the ration, fresh new art, colours, architectural styles, the NHS was fresh, exciting, and new, the brown of WW2 was being painted over with what must have felt like the future to every home.
Imagine seeing a PA Cresta, a Vulcan bomber, a High-rise block of flats, TV, technicolor Films for the first time... and then going to the doctors, and being treat using brand new equipment, for free, when the likelihood was your grandparents died because they couldnt afford the medicine. Must have felt incredible.