This is a post about a significantly larger scale issue regarding server economy, but my suggestions has to do with dungeons or duties.

Currently, there is massive gil sink right now at end-game (Repairs, Portals, Ferry, Gearing), and there is not enough gil injection. At the point in which you reach level 50 there are a finite amount of quests left for you to profit from (Gold pieces). Crafting materials, and gear you no longer need or can't use either sells for pennies at the vendor or it is unsellable at all. Leves provide little to no return, when compared to the repairs incurred from doing them. Fates are of the same consequence. At the end of the day when farmers, miners and gatherers are selling their wares the money they are making is coming from players who have earned their money leveling up to 50. However this is gil being taken OUT of the economy. And this money will never be replenished.

TL;DR - Too much gil sink, not enough gil injection at level 50.