If it requires Ingots or coupons it's best to be avoided and instead save the currency for other ways to get stronger, like Dice Board, using scrolls in lots of 10 on treasure is completely worthless, all of those Ninjas in the "Seal Treasure" are free characters the game will throw at you, waiting until you have 60 or more scrolls and have Sage or better yet Kage treasure unlocked would be a lot more effective. (Tendo treasure is also not really ideal to use scroll on but not too terrible either)

You can highlight them with the mouse and it'll tell you what you get usually.

Usually i save all my coupons for Lucky Board because when you think about it, you're generally getting alot more back than what you put in, between stuff on the board, lucky Ninja boxes and the points used for things.