As a general rule, buying points is only a good idea if you need a few points extra to book a reservation.
Pick a flight that you would potentially fly in the future. How many points does it cost versus how much would you pay in cash? Then calculate how much it would cost to buy the points for that reservation. Every time I’ve ever done this, it was always more to buy the points than to pay with cash, even when there were sales. YMMV but it’s never worked out mathematically for me.
Yep even with their current special offer it’s still more to purchase points than to just pay for flight.