When I complete an event that rewards a chest/any loot, does the quality of the medal received (Bronze, Silver, Gold) affect the quality of the loot received? Or does the medal only affect the amount of EXP/Karma received?
From experience in doing the various dragon events, no. Medal quality does not affect loot from the treasure chest after the end of the events.
I have got rares from events where i only achieved a bronze medal and vice-versa.
I don't think there is any real and concrete evidence to prove this at this point in time though.