[logfromblammo]

The person who casts the deciding vote probably won't know that they had done it, so that vote could also have zero value. All they know is that the voted for the winner.

Every vote in the entire election could have zero value, if none of the winners change their political stances as a result, and public policy is essentially unchanged from the period before the election.

That's why I see votes on a binding referendum to have more value than races for office between two essentially indistinguishable candidates.