Market exploded late 80s so before then, 1984/85 my guess ?
E Types have an unequalled magic, charm and charisma especially for those who grew up in the 60s/70s.
I have owned all variants from 1963/74 S1/2/3 cars, roadsters, coupes and 2+2 in 3.8, 4.2 and V12 guise. All have different characteristics and reflect similarities to the Z/ZX S30/S130 lineage in that the earliest 3.8 cars are the purest and rawest sports cars that later morphed into the V12 boulevard cruisers.
These days I prefer to own and drive S30 as a choice of preference, nicer to drive and a lot cheaper to own, win/win.