31 cp/pt would give you more value for each point spent that 24 cp/pt. Usually, events where I post this are ones where you can't spend coupons to gain more points, so it is more how to get the most value out of your limited points. But, sometimes other things are more important. For me, if it is a choice between 3.8 and 3.4, I might go for the 3.4 item/ninja if it is something I want. But, if the choice is between 8.7 and 2.3, I might have a hard time grabbing the lower item even if I need it.