Rule 6 hasn't killed the arena all by itself. Was really just the last straw that broke the camels back.
The war scoring system + the economy + field and plane placement + milk running complaints + player interest in furballing vs warfighting + no casual play.
All together = an empty arena.
Scoring:
I still agree that the war set up is the way to go. But until all aspects of play directly contribute to the final tally there's no point in doing the was set up. Furballers kills need to count against the score.
The score doesn't need to effect the economy. Rather than lowering the economy from week to week, just tally up victory points each round.
Economy + Field & Plane Placement:
No one is happy with this aspect. It is obvious now that peoples interests are flying the planes they want to fly. The war is secondary. In order to fly what they want to fly, and not have to burn an extra half an hour flying from rear bases the players have spoken. They'd rather just go to the other arena's.
Using the same spending model we have now I suggest this change. Increase the current funds. Anywhere from 50% to 100%. We need to be able to fly more types of planes from more places. In addition each choice now populates 3 fields. So for the same price that you put down 1 BF-109K-4 before. You now put down 3 BF-109K-4 at different bases.
Another idea is to have all planes available to a side, available at all fields. Or at all fields they purchase. (Requires splitting up the funds into categories, or setting a price for air fields/vehicle fields/naval yards, an adding them to the list.)
These should help increase the casual play aspect of the arena. If playing in the arena is a hassle or too much of an inconvenience the players will go elsewhere. You can't plan it out completely like a scenario in the way the FSO runs. People don't have time to play something like the FSO every night.
Milkrunning Issue
This isn't an issue with the above implemented. You only feel the milk running aspect when you have such limited spawn points that the enemy is able to knock you completely out of play. Milk running was a side effect of the economy. Increase the launch points to the point that it is impractical to even attempt to knock out the other sides ability to lift off and the problem goes away.
Even if it wasn't the players need to understand that there are no such things as off hours. It's a 24-7 arena. There is no time you could shut the arena down that would not be unfair to some chunk of players. Prime time is different even for players in the same time zone.
Besides no group of casual players have shown the ability to stop an organized bomber raid. Those same 5-6 players accused of milk running could get together and run that same B17 raids at 6PM PST on a Friday or Saturday night with 50 people in the arena and the bombers would still get through with minimal fighting. They might not make it back to base, but short of blind dumb luck by the other side they'll get through to their targets.