One thing worth noting, this event has a lot less value when using coupons instead of ingots. When using ingots, you get basically x3 more gain because of all other spending/recharging events that go along with it. When using coupons, you dont get anything else other that tree rewards themselves.

Over the whole week you should be able to get at least 49 free uses (7*6 from dailies and 1 free, +all those from world tree), which will give u +- 100 points and a few keys/moods/refines/charm frags. You can invest those 100 pts to get additional 33 keys, or 2-4 other ninja frags. Overall you get between 500-1000 coupon value for free. It's a nice event if all you get is free items. It's good as well if you go crazy with ingots. It's simply not designed for coupon usage or low to medium level spending- it's either go free or go * spending.

Free value from that event is comparable to that from survival trial missions where you get seal scrolls- and people never complain about it. Just do the math.