If if if if if if I'll do that (time and money are, unfortunately, limited), I'd focus on single decades too. The evaluation I'm doing is now on the most recent: 2000-2009, with the idea of coming back later. And the first sensitivity is that even these single decade has seen about 500 different concept-cars.
Hence, I'm wondering if electric versions of regular cars or anticipations of regular cars are actually interesting or if it could be better (and lighter) to focus only on "real" concept cars.
And of course only the ones made by real companies (not self-made attempts) or shown at major shows.