For once, you are more positive about changes than I am haha. I joke I joke.
Alright, let us consider the Arena from a different point of view. Let me consider the Arena from the best possible angle and consider the potential that it has. This, for me would be the best case scenario. @Thor von Blitz said something that I enjoyed, that the Arena would have challenges that would be weekly/bi-weekly that would reward you for doing this gamemode. Similar to the Bilge Rat Adventures.
The Biggest problem I have with this gamemode is that it is not immersive. It's separate. Something to the side. You select it as something seperate, rather than (which I would love much more) this being something like the fighters guild? (I forget) in World of Warcraft or the Arena in Fable. Something you can choose to do, like a new kind of activity.
Best case scenario to fix this, in my opinion, would be to allow players to go to the man in the trailer (I forget his name) who changes your location to match you with other players that want to do this as well. Thus, earning reputation with the faction makes sense as he would just gather pirates who want to compete for treasure.
I hope the competition of this game-mode/voyage would lie in literally competing for the same voyage. Man in trailer gives everyone the same treasure map, and gathering the most makes you win. Thus, as you said @KnifeLife Rare could expand upon it for this man to offer you even different kinds of voyages/events. Perhaps you can pay the man to bring a bunch of pirates together so you can, as you said, host events. Or, perhaps Skullball or Beacon Brawlers, En Garde, actual Ship Races, Broboat Race, Rum Runners etc etc could all be included in this game-mode.
The gamemode is called Arena, thus, for me, the dream would be that it offers actual Arena modes that are an addition to the Adventure Mode rather than something seperate. Perhaps taverns are expanded to include an area where you can go to participate in the Arena. But, that is unlikely and never going to happen for various reasons as described in a tweet by @MikeTheMutinous and a post by him in this same thread. However, even if some of this would be included it would be a major improvement for me. Make it something that is an arena also built on things players have done but also just different kind of challenges, but that's just my opinion.