From what I understand, using gold efficiently will be your last worry. What you want at first is to upgrade your hoard quailty to level 10, so you should always bring in 5 treasures in any combinations that result in 100% quailty upgrade success rate. You have to make the best of what treasure you have, without worrying too much about gold, which can come in any modes, while treasures are exclusive to Delve.
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Sacred Treasure ×5 = Awesome!
Most effective way. You got maximum exp and % quailty chance by using minimum gold -
Sacred Treasure x2 = Okay.
Maximum % quailty chance, but a bit waste of treasure and gold -
Priest’s Chalice x5 = Nice.
Easiest maximum % quailty chance. Minimum gold spend, but using lowest Tier of treasures possible, so you get much less exp. -
Sacred Treasure + Genie’s Lamb + Gold Ring + Coin Purse x2 = Nice.
A bit complex, but still get maximum 100% quailty chance. Minimum gold, but lacking in exp. -
Coin Purse ×5 = Not good.
While you spend the less gold, your quality chance is only 25%, so it bound to fail. You get a grain of exp. as well. -
Coin Purse x1 = Bad!
You just waste your gold on entry fee, and get screwed by 5% chance. Better save it for later and combine with other Treasures.