score:4
I'd say buy your tickets as soon as you are sure you want to travel on that day.
While sometimes prices drop dramatically, most of the time they drop only a bit and the early buyers are getting better prices.
I have no experience in South America, but as you need to travel to those events, I would not trust there to be cheap tickets.
Upvote:2
If the price drops rapidly, it can be risky to wait till less than a week before your flight. After all, you may end up paying even more, but it's your choice.
A good idea is to create price alerts on a few websites like Google Flights and Skyscanner and buy the tickets immediately when the price starts dropping/when you see they are at a reasonable or average price, you don't know what could happen.