I have finally started hoarding GW mail past 6 months or so, cashing in at contest time. It's supa annoying.
I wish the game would actually punish hoarding. For example if a player holds GW battle reward mail past 6 days, not only does mail expire but the account is deducted the amount of tokens and gold. A nice explosion or whammy sound would be nice when they go poof so that the offending player's gut sinks. Big, bold, red font, in maybe a devilish font face, could report the bad news in a piece of mail that never expires as a constant reminder of the offense. Infinite negative values possible so that deductions can create a deep hole that hoarders must climb out of (just like real-life hoarders eventually must climb a path out of their junk hehe).
My friend Nofshmeer once collected so many empty bottles that when he tried to escape he needed to get to his icy mountain climbing equipment, but when he tried, the bottles started rolling like a conveyor belt and he slipped and bonked his head. For the rest of his life his brain was all messed up--he would pace around muttering absurdities like Ashton Kutcher is a talented actor, Amy Schumer is funny, and Drake has elevated the rap game.
Anyway the bottom line is that hoarding should be ended with immediate punitive measures. This would encourage people to actually use their resources and to push their resource management to another level.