What if we went the other way for a solution? Instead of simplifying a Coliseum or building a new one, ...how about a marketplace instead? Think Secret of Evermore; up front pricing, shopkeeps extolling the virtues of wares, the option to require more than a 1:1 trade (an option for GP sink, or swapping around consumables like 1 megalixer for 10 elixir). Or token exchange replacing boss drops (Blue Dragon drops B.Scale, can trade in for 1 of 3 gear. All of which can be circular-traded in market at some small cost).