sun coins imo should only be spent on advanced refines or scrolls for assist links...moon coins is a tougher choice since you have more in there that u would want i usually go all keys best option unless the rebate changes...im trying something new this go around, im saving keys till 2100 but only doing 1050 on the next rebate then i will already have the 1050 i need for next month so i can spend a whole month in between using moon coins on either bells, 2 chimes, but most likely ill prolly go for advanced thread. Then when the next cave key rebate is around ill have my 1050 already then i can go back to getting keys then rinse and repeat the process...i also get keys from the wish tree instead of coupons since the value of the keys from the tree are more than double then what u get from getting the daily coupons....