I just re-read your original post ... so, to address some of your points:

'I am simply somebody who does not "get" "Blowin' in the Wind".'

"Getting" and "liking" songs and poetry is very subjective - what is striking or appealing to one person may well leave another cold.

'I know these are not original observations but to my ears it is simply a list of rhetorical questions'

Agreed - except for the adjective "simply". The rhetorical questions are in the form of remarkable, memorable images and phraseology with Churchillian power -

'culminating in a phrase that is so vague & imprecise that it could mean whatever you wished it to.'

Not quite. Despite some of the preceeding interpretation, "blowin' in the wind" clearly indicates that there are no easy answers; perhaps there are no answers - but the rest of song implies the desirability of trying to improve things anyway - much like the refrain "when will they ever learn". The "failure" to provide a pat answer is one reason why this song lives on, and will live on long after those anthems that celebrate pat answers have been discredited and forgotten.

'And yet it seems to hold a special place in the affections of a great many people.
Is this because of the way it was picked up by Civil Rights movement'

There are many reasons for the popularity of the song: nostalgia combined with its association with the correct causes of the '60s & '70s being only part of it, although perhaps the main part.

'or is it because of some particular merit of the song which I have failed to notice?'

There IS considerable merit in the song - FOR those who are moved and excited by imagery and the imaginative use of language. That's not everybody. For those who are more moved by straight and effective logic, the song will have less merit.

It's like the vintage car the mechanic down the road is always tinkering with. How much merit is there in it? For me, not a great deal. For him - clearly, a great deal. Which one of us is right? (The answer, my friend ... ).