Theory I've been messing around with, not sure if accurate.

[Kuurei]

Was playing with a friend of mine yesterday evening and noticed a massive spike in loot quality when partied up, we got 2~3 golds a run in some instances. My character I've been solo'ing with however rarely gets anything over a Bronze from instances, or the occasional silver. I also think the EXP is going a bit faster grouped, feel like we got a bit more per dungeon due to the pool.

Not entirely sure if this is accurate, but I think if peeps ran around in maxed parties they would see a pretty good upscale in loot quality and dungeon exp (definitely does not apply to quests).