Been wondering about this myself. I'm at about 40 hours /played and I haven't even seen an epic/purple yet.
I'm only on continent 2, but given my playtime, I guess you could say I have done a considerable amount of exploring, and from what I have heard, the coninent level doesn't affect enchant quality.
I am going to go ahead and update to the beta, I read one comment noting the drops are a bit better in the current beta, so I will try that out.
I have been wondering about the chests as well, I have only seen small ones. Those seem strangely as well, some areas I see 2 in almost every room, in others, not even in the stash rooms. Not sure if there is a pattern, they seem to only appear after the first 2 lieutenants are killed, but not at all after 3 or 4 are down, but I am not sure about that.