Voting is mentioned in Losing the Peace,
in the context of a refugee who didn't submit a vote in the last election, figuring that no matter who was in charge the Federation as a whole would go on "normally". And in the afore-mentioned Articles of the Federation
a child asks her mother who she, the mother, voted for, and concludes from the terse response that it was the losing candidate. So the issue does come up in Trek lit from time to time.