Unless I am missing something your math is a little out. A 20%discount is equal to a 25% bonus, while a 30% discount equates to a roughly 43% bonus.
Hmm, good question.
In general, a bonus is worth around half the same percentage of discount as long as points cost a fixed price.
For example, say that points cost $20 per thousand and you buy 50,000 with a 100% bonus. You spend $1,000 and end up with 100,000 points.
Instead, say that you buy 100,000 points which normally cost $20 per thousand, but at a 50% discount. So, you pay $10 per thousand and get the 100,000 points for $1,000.
This is exactly the same as the first scenario.
I just had a look at some examples with Choice Privileges, though, and you're right that it doesn't quite work out this way because the cost of points changes depending on how many you buy.
For example, with Choice, 24,000 points cost USD247.20. At a 30% discount it costs USD173.04 and you get 24,000 points.
Or if you buy 15,000 points at a 60% bonus, you also end up with 24,000 points. This costs USD154.50 for 15,000 points at full price. Which in this case is a better deal.
So, fair enough
@drmatte