The only format that small, closely-knit together groups shine is tPvP.
And i don't really see it as a bad thing. Even if you have 6 friends who enjoy playing together, there's nothing wrong in joining something bigger and established with all those 6 people. Not like the leader/officers can force you to group up with other guildies if you prefer to stick to your 'original' group. Then again, even in a big guild with 50+ active (and representing) people, sooner or later you will find several more or less like-minded players with whom you'll enjoy grouping the most, and will tend to group with them. It does lead to fracturing a bit, but it's within the human social nature, and there's nothing wrong about it, really, as long as you're open to play with other guildies as well.
Now about w3... random zergs are usually bad and easy to beat down with smaller yet organised force. 30 random, upscaled people will die to even a bit coordinated group of 15. But now imagine a more or less coordinated guild group of 30...
The real question is - how many buffs do you maintain 24/7? Do you run +karma, +xp, +magic find and +gathering all the time? We do, as a bigger and more active guild, with still 30k surplus influence and rising, but i remember times when i had to juggle the 'current upgrades' not to end up with 3k influence.
Yep, karma, magic find and gathering boosts are active all the time, and we restock/use banners on a daily basis.