Interesting thought, though a server-wide battle sounds alot like Ragnarok.

Benefits of a server arena would be incentive for the top of each realm to be going head to head. Especially if the rewards were better. Also, it would allow active players that are "stuck" in their current realm arena slots because of large power gaps to bump up a few places and increase competition/growth in each realm too if people could enter the multi-realm arena. Maybe there are only a certain amount of spots in the server-wide arena, and once you get bumped off you get sent back to your original until strong enough to try again or after a cooldown period, allowing people to decide which arena presents the best opportunity.

It seems like the hangups to that would be making Rag somewhat pointless, and how it would impact people switching realms to chase 1000k gem stakes. I don't believe it would be fair to allow people in more than 1 arena otherwise you'd get the tops raking in rewards from both. Also to some extent Tynon would lose the realm switch fee for people that jump to get better arena standings, though I think the overall increase in competition would lead to faster growth. As it is there's little room to grow for people joining a server late or underpowered, which leads to the current server dash.

I believe mixing it up and creating competition through multiple standing venues such as arena would encourage server longevity and more vertical vice lateral growth. I.e., more people sticking around instead of running off to the next server. Rag won't do it, because the nominal cred and rep gain for one event a day is almost pointless there. Fluctuating profit margins and the possibility of disconnecting and negating any gain your boost gets you discourages it largely. Guild Wars is a collective event in which you don't really need to win to benefit from. Arena however, is where you can make large amounts of personal coins, creds and rep daily and offers the best advantage. It is buffered from the DC factor because you have 24 hours to climb up the ladder or 24 hours to worry about holding it. It's where I see the most competition. I think opening the competition wider by having both a realm and server arena would make things more dynamic as well as negate any realm switch fee lost. Afterall, you would still have to jump realms to chase the 1000k gem stakes, and if there's a cooldown period then others might be able to grab that sweet number 1 server spot for a day or two.

Anyways, a really interesting idea. I probably put too much thought into it.