Lacking any sort of political or sociological expertise, i try in public forums to avoid commenting on those sorts of issues...
But one other thing Jeremy's post highlights (to me) is that retiring in a year like 1966 didn't work out well as much for socio-political reasons as anything else.
I.e., the country was in crisis. And the economy (and the capital markets) simply reflected that.
Not sure how actionable that insight is... but as I think about it, it makes me worry less about a richly valued stock market... and maybe more about the other issues we as a country or world are debating.