I wouldn't mind if stuff spawned in the gold key vaults if everything that spawned dropped something
by time people get to gold key levels they should be able to handle the riddle quickly and get all the decent stuff out with time to spare and more drops would be nice
now that I think of it just tie it to picking up the ancient chest. If people know what they are doing enough to get the tribute chest they can handle a few monsters and get the extra loot
and people can choose to grab the chest at whatever point they want which will give people the option to fight more or less