What if there was a system that allowed you to participate in content as much as you wanted with whoever you wanted, but prevented people from obtaining loot and selling runs?
How about infecting players with Allagan Pox?
Allagan Pox / Status effect
A plague that has not been successfully cured and can become contagious when surrounded by crowds of infected.
Okay....so the description would need a lot of work, but what does it do? Having Pox will prevent you from being able to lot on loot within a particular turn and is obtained after leaving the zone (whether you obtain the loot or not).
Pox would also be bestowed upon players should they enter an instance with at least 6 other players who possess it. Why? To prevent parties from "selling" runs for gil. There could also be a message in the confirmation window upon speaking with the npc to verify how many players possess the Pox while not specifying who has it to prevent harassment.
This will give parties a chance to redo the content as they see fir while keeping the income of loot under control by preventing players from monopolizing the instances for gil and loot.
So, what'cha think?