The question if spending more to get more points is an interesting one, and there’s not really a right answer because it all depends on how much extra value you can get for the points you’re getting.
Different uses for your points represent different value. To figure out if the extra spend is worth it for you, you will need to assess what it is that you plan to do with these points that you’re earning, because the value of the reward relative to the cash price if you bought the same thing will show you how much your points are worth and whether or not it’s a good idea.
Without knowing what you’re saving for I’d suggest it’s probable not worth it, but as I say that may differ depending on what you plan on using the points for.
For example if you were using these points on an award seat SYD - SIN one way. It costs 28,000 points for the seat, and you’d be getting an extra 13,000 by going the flexible fare, so the points you’re getting equate to 46% of the value of the redemption. The cash price on a one way is roughly $550 give or take, so that means that 46% of that $550 cash fare is $253 - effectively the 13,000 points is equal to $253, but you’re paying an extra $600 to get them. In actual practice it’s slightly less than that even, as on award seats you will also pay fuel and taxes on top of the points.
If that was how you planned to use your points then it’s absolutely not worth paying the extra, but as I say different uses and different redemptions offer better or worse value so depending on your intended use for the points it may be worth it.
Hope that helps!