I've just been stockpiling my coupons as well.
I'm at around 1,170 coupons right now. . . .
It's tempting to buy a couple more summoning/seal scrolls for the x10, or purchasing some magatamas/runes. . . but I think I'll save until around 2,000 and see what future events hold for us. :P

Some People recommend indeed to use the Coupons for Magatamas, that's something you have to know for yourself tho. If you want to compete with others then Magatamas are a must have, if not then you can just collect them through Ninja exam and other stuff.
Some People recommend to save your Coupons and Seal Scrolls till lv50, at lv50 you unlock the Tendo Seal Treasure that can give you all the Pains "easier" also it has some other Ninja's in it that the old Seal Treasures don't have. If you want to gamble and are okay with staying with the starter Ninja's or the ones you get for free from the Game, go for it~

Buy magatamas, be on the top, take top/high difficulity level rewards.

My opinion (consider,I am just one week in the game)

Refining and Magatamas you need to be stronger or you can save them and buy some ninjas with them when new events come....80 frags for 1 ninja is 3200 or 4000+ coupons or ingots...

Deleted as posted in wrong thread.
This post was last edited by jam***@hotmail.co.uk at 2016-8-8 19:57

1) refine
2) power-wise? not very significant, but the stats are very crucial in battles, since winning rate is often dependent on your initiative (attacking order) where being able to attack/use your mystery first may allow you to prevent your enemy from taking any action. Having a high initiative is one of the most important way to beat players with a stronger power than you. Not saying that power is not important, but magatamas may be attained very easily from ninja exams, where refine runes are more difficult to get in general.
3) or you c*so save your coupons for future events, because most of them will require a ton of coupons if you wish to exchange for ninjas/other things