I completely agree with this. While I don't know how well it would work out with different games, I can definitely say that event servers are one of the more exciting things in this community. Remember how hyped everyone was about DoD when it was first announced? Yeah, that was because it was new. Now that we've all seen what it's like and experienced it as much as we'd like, the numbers are dwindling, because it's not new and exciting any more.
Same goes for A&T and probably Infection as well.
Now, I'm not saying that DoD, A&T and Infection should all be removed from the line-up, not at all. I'm only saying that the hype wears off in time, and that event servers should stay temporary. However, that's all the more fun from them, because in the short time that it is new and exciting, lots of people will be on those servers and honestly, I don't care about what the server is about so much, I care about the people I play with. The people is what makes the servers interesting and fun, and event servers draw in more people. Therefore, event servers tend to be more fun. And if we get them frequently, then I think it's safe to say that the fun that comes with them becomes frequent as well. Not too frequent, people would like to catch their breaths between event servers probably, but maybe with a month between them, if that is possible.