An Inside Job

Currently you can abuse the group finder's cross realm feature to easily finish the quest in less than 2 minutes without having to deal with the currently buggy mechanics:

1. Start the quest and stay out of range of the first guards, no need to kill any of them. But be sure that you're in the quest area with the assignment of getting the "Iron Horde intel". (You might need to enter the area once to finish "infiltrate the compound", so you get the next assignment)
2. Find a group in the group finder from a different realm and join it. (Auto-invite groups will do just fine.)
3. All the mobs in the area will despawn and you can simply walk straight to the building for the intel, just go down the stairs.
4. Leave the group and a single mob will appear. Interrupt and kill it and take the Iron Horde intel from the table.
5. Repeat step 2.
6. Walk the way up and stay near the first cannon/crates near the edge of the wall.
7. Leave the group and a big crate pile will spawn in front of you (when facing away from the wall). Click it and the cinematic will start after a ~1 second cast.
8. Enjoy the cinematic and the fact that you just saved yourself hours of frustration.
9. You might need to relog to make Khadgar appear and finish the quest.
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edit: looks like it still works on 6.1.2 as of 4/28/2015

If you use Aviana's Feather while in the compound, Khadgar will port you back down and berate you for it:

Archmage Khadgar yells: Are you crazy, launching yourself into the air like that! Why not just send Gul'dan a telegram? Better yet, march into the compound at the head of a Brewfest oompah band. This is a stealth mission, <name>! Stealth!

100% worth doing at least once just to see this.

Easily the worst quest I've ever done in WoW. Tedious, boring, and buggy. Sit there for ten minutes, click a button on an NPC. What a wonderful legendary quest.

I sincerely hope whoever designed this was fired.