Stranger in a Stranger Land was probably more of particular time and place that a lot of Heinlein's works. Although it came out at in 1961--mostly predating the counterculture era in the US, its mainstream cross-over appeal was definitely tied in with the Summer of Love etc. later in the decade.

1968 would indeed be about the right time period as "I grok Spock" bumper stickers appeared around then too.

happens that it was banned in TX schools until 2003, so i guess some share of population just doesn't grok it :)