I never sell lvl60+ stones, the zeni I have is mostly from selling junk, I use every single stone I get on my own gear. It is frustrating to spend days farming only to end up with a worse gear + than I originally had before I started farming. Basically it IS frustrating to go backwards when you are spending time playing to achieve some progress with your character. Personally the 100% RNG dependency is what is driving me apart from the game, this game needs to reward players based on how much time they spend playing the damn game for once.
also
*flashbacks to the missing tradeable CC mats poll by the staff*
I never sell my stones too, but is so annoying get +1 when u try +9 to +12.
Anyways upgrade is too easy, on Taiwan was hard get +10, here is easy make +12, hard are higher upgrades...