As f2p player i have 1500 coupons too, but... i'll keep them more. Really, even if we spend all this coupons refine/clothes, we still cant beat p2w. Just cuz they spend more and have more stuff. So what we can do?

For me the funniest thing in this game is ninjas. Create new lineups, do experiments with them. But as f2p players we cant have all characters what we want. So my advice - keep your coupons, and later on events you can buy any ninja what you want.
P.s. Max magatama's lvl i've ever seen - 8.