It is honestly a quality over quantity question. In about 2months with free seals from events and daily things i think it might be better to buff up your charms since it just released and they are currently selling at 100 for 1 of each. with all the systems in this game u hit a soft cap where the investment can be better spent elsewhere. If u have lvl 5-6 runes from cave then id say its a bad investment. if u made progress at getting your move 1 at least to a very high charm level u will have the priority in combat and hold a superior position.