We always do "guild vs. player" for any decent size raid. One reason is that it goes faster (time is already essential; we need to finish before a guild mate of the target notices). Another reason is that it's easier to have enough turns when we're more players. Oh, and it's more fun that way, of course!
As for the defense: Any player who's done training and reached a decent rank should always help. I know my guildmates are both able and willing to do so. As I would myself. Don't wanna help a guild mate under attack? Find an other guild. This is true for most guilds (I have seen exceptions, but they are rare). SSTG are famous for looking after each others, for instance. I always expect one of them to watch the guild page around the top of the hour.
Guild vs guild battles may sound fun. And yes, we already have the tools. What we lack, is incentive. Why would the T'zak Ryn attack AYES? Not much to gain from that. We may gain from lighting up and plundering one of their players, of course, but declaring and conducting an all-out war on their guild would simply drain our resources (and theirs), giving us nothing back. We'd only do such a thing as part of our contract work, but that would require someone ELSE to have a reason to want to drain the resources of our "target guild".
Then there is the nation/guild discussion. Some may feel a stronger bond to their nation than to their guild, while it's the opposite for others. This causes a messy situation. I know a player got angry when one of my guild mates stole two ships from him, because they were in the same nation. Our reply: We are loyal to the T'zak Ryn only, and don't care about your nationality. If he considered his nation to be his "friends", that might be tough on him.
If you want more nation vs nation action, or guild vs guild, then this "Am I loyal to my nation or guild?" situation may need some sorting out first. And there needs to be a REASON to attack another guild or nation (there are some small reasons to attack nations, but not really to attack guilds). I believe that a simple, yet effective way to achieve this would be to implement something along the lines of "External Political Events" (
viewtopic.php?f=4&t=2591&p=32742&hilit=External+Political+Events#p32742). Want a war? Give it as a "quest" to the leaders of a nation, with rewards for success and penalties for failure.
Apart from that, I'm sure new ideas to mechanics will come from both me and several other players. But as it is, with no new mechanics, I think our raids will become even rarer than they already are. Probably there will be none until we come up with more mechanichs which benefits the attackers in raids. Or if call levi and ambush cards become "common".