NOE missions are super easy to bust, and they get clobbered all the time. All it takes is one LA-7 to come screaming out and go right for the goon, which is the Achilles heal of NOE missions.
Or if one person sees a base flashing without DAR they can be fairly sure an NOE is coming in. All they need to do gain about 3,000 feet of alt over the base, of which there is ample time to do so.
Once that happens, the NOE mission is helpless. They are low on the deck and can be picked off one by one with B/z attacks. I've seen it happen countless times.
Base and town begin flashing once any element of the NOE is within dar range. Your typical NOE will be 110's or Mossies, and that gives about 5 minutes of warning before they can get to the town.
In other words, the NOE is not some quirky part of the game that can't be foiled.
If the win-the-war and land grabbing isn't your thing, NOE missions just are just boring as hell. I mean you shoot some buildings and make a capture.
As far as 'spying' is concerned, I don't believe it happens all that often. Mostly because I think it is boring duty for the 'spy'. Most people just want to play, and who really cares 'that much' about map resets, there is just another map to follow until eternity.
The reason there are no 'rules' against spying however, is because it is impossible to stop someone determined to do it. Even if cross country comms between players was removed, how would you stop someone from calling their friend on a cell phone.