I plan on starting AoW in a couple months, and also thought the "hook" for the entire party was a little flimsy.
What I'm thinking of doing is having the Seekers adventuring party have only written references to the location of the Whispering Cairn, and they hire a local to help them find the referenced landmarks. During the search process, the guide realizes one of the landmarks (a lammusa statue) has fallen into a ravine during a small landslide years ago. The guide convinces the Khellek and co. that the statue fell from the west side of the ravine, when it was actually the east. So the guide has a better idea of the true location of the Whispering Cairn, and the Seekers are off on a wild goose chase.
The guide shares this info with a friend (a PC), asking him to find some people to explore the cairn with. Have them meet at the abandoned mine office.
Unfortunately, the guide also stole a potion from Khellek, and Khellek kills him without finding out about the guide's bigger betrayal. So the party will be left waiting for him at the office.
The obvious magical nature of the guide's death will cast some suspicions on Allustan.
Now, the AP is designed to cover 20 levels in about 12 adventures. Assuming 13 1/3 encounters before leveling, we're looking at approximately 22 encounters per adventure. Obviously this isn't happening. What's the AP missing? Sidequests.
Hmmm... but isn't that 13.333 encounters of CR=Avg Party Level? Throw in a few higher CR battles (as Dungeon does) and you don't need as many. Also, I tend to pad out XP with story awards anyway, especially after an adventure's climax.