Pauses and Punctuation

The semicolon and comma are the best option. You have two independent clauses, one of which elides the subject and verb, so you use a comma to indicate ellipsis.

I am optimistic; Kevin, pessimistic.

Ethel lived to be ninety-one; her husband, only eighty-six.

This is noted in the Chicago Manual of Style §6.49, “commas to indicate elision”.

If I were writing it, I would go for your first suggestion, and simply omit the second comma. Whilst convention may say it should be there, there is an overriding requirement that punctuation should guide comprehension. That is my own view.

'Curiosity and diversity were discouraged, at times disciplined.'

It seems to me that the correct way would be to include an and like so:

"Curiosity and diversity were discouraged, and at times, disciplined."