Use them in fair i would say , try to aim for the 1.8 million for 10 gem gold offers. There is no need to use it on mystery box ever or cooldown resets. Also try buy the blue stars to go for 2-5 gems each , really handy for extra power! and if you in the top guild of your realm then using the shrine is good for gold / creds when u need it , up until the point where the cost increases to 2 gems per a go .