Would this be a fixed amount zapped per vote? This would ensure a certain amount of interest in the matter and prevent bots.
Without a fixed zapping amount you would have less of a voice if you are poor.
Discussion
While I agree that would be nice to have some fixed value for each vote(decided when creating a poll), it's not a big deal not having it. Spending a finite money to just to change a poll on nostr? Have your way sir.