I was thinking of opening a new topic in Suggestions about this post but since there is a conversation here with a similar purpose, I guess it is fine. I think there is something "missing" from the game. What we call money-sink. Let me explain.
Normally, when there is a steady turnout of new players in a game, it can become tricky when they have to compete over the same items with old players that have greater income, in more than one ways. To counter this, most games invend of a way to make older players spend their money in other things and ease the new players a bit. There are some money-sink mechanisms in game, but seemingly they are not enough. The problem with the existing such mechanisms is that they apply in both old and new players. Both repair their equipment, both pay their mercenaries, both buy their potions. What this game needs is something that new players can't have and old players want to have.
One idea is to implement achievements. Finish x dungeon without using mercenaries, kill y bears, etc. Some of the achievements though can be something like use z items at once, or even buy t random worthless items with hopes that they'll unlock an achievement in the future.
Of course, this is just a suggestion but I think it would lead high-tier players spend a part of their money so they then have less money to invest in diamonds, leading in a price drop.