Having flat currency is never going to be too rewarding since it can damage the economy, they just wouldn't allow it.
They could make the reward for Red an option to prestige, resetting the stories and possibly making them harder each time(higher levels or just handicaps) with some sort of visual reward where players can see it(like an icon next to your name).
I mean, I personally would never like to continue doing the storyline but I'm sure some of the PvE folk would like it lol.