Refinement , Rune Stones and Charms should be your priority. Use them ONLY during rebates. I would say for refines and charms hit he max on the rebate 500 refines and charms for both rebates as they give a lot back. For rune stones aim at least to hit 500 cave keys used during the rebate , gather cave keys from your wishing tree and you can buy cave key gift pack during rebates which gives 88 cave keys + lvl 5 rune stone for 900 coupons.