Maybe one kind of event or special missions to spend stamina .
would be great.
but I think for now they do not do this yet.
Not have many players who completed the 3 worlds yet, and this would sub-divide the use of stamina between the event and quests.
As there is no way to buy anything in the game. Doing some kind of event or special missions with cost of stamina would benefit only those who completed the 3 worlds.