I don't see any problem with having more than one arena. I personally enjoy switching between Late War, Mid War and the Axis vs. Allies arena.
One thing I do think might help, though, is to combine the two Late War arenas when there's not many players up (and that's coming from someone who does not like Titanic Tuesday). Sometimes, if there's just a handful of people in the lower populated LW arena, it can be a chore to find a decent fight.
Don't know how that would work, though. You'd have to decide when to combine or split the arenas based on a certain number of players (what that number would be, I have no idea) and, it could end up being a mess if the arenas had to be reset often.
