Adding a level increase sounds like a reasonable thing to do at this point. With that in mind, also create another tier with the epic boss event to follow inline with the max level increase.
tier 151-200
tier 201-250
tier 251-300
And with that max level increase, make an adjustment to the "whale" zone as well. As a matter of fact, remove the whale zone all together. The rivals that you see should be based on your level and the number of allies that you are currently holding.
Inventory sorting - Yes, please..
Black Market sounds fun, but could get out of hand easily.
My2cents