Planescape: The Age of Worms

I've never played or read Savage Tides, so I can't really comment on that.

I'm not fond of the initial hook for the Whispering Cairn, its the only week part of that adventure. The best I've seen using  it was a group of PCs who decided that they weren't going to let a group of outsiders raid the Cairns and that the people of Diamond Lake should have the treasure if anyone does. In a pinch, you give them the hook that some Primes are going to go treasure hunting in the Cairns, and it should be enough for any Prime to want to keep those treasures out of the hands of those Clueless addleheads. A more Planescape way to do that would be to say their have always been rumors of a great thought hidden in the Whispering Cairn, a powerful idea or secret that would be the road to greater power and understanding. Many have tried to get in and find it, but only the PCs are able to manage it.

 Also keep in mind that I'd say that the PCs should either be natives of  Diamond Lake, or Primes who happened to stumble in there as opposed to cutters from Sigil.

 As for longer term motivations, your right, Kyuss rising likely won't be the end of the Planes, but that doesn't mean that the heros cannot oppose him. It didn't stop the heros of Dead Gods, did it? Personally, I would try to hook them in by making it personal for the heros once they stumble onto the plot. They want to take these berks down for what they've done to them, in addition to the whole saving people thing. If any of players are from the prime, word could worm their way back to them that the spawn of Kyuss have begin to appear on their home. If Kyuss accends to full power, their entire world could die! The Kreigstanz could also play a role, especially Pre-Faction War, since Kyuss's rise to godhood could be seen as proof of the Believers of the Source's creed and any number of Bleakers or rivals from other factions may seek to put an end to it. 

 I've currently got the ascension occurring on one of the cubes on Acheron in order to bypass the Lady. Plus it adds the dramatic tension of the entire cube trying to shift to a different plane to become Kyuss's new realm and the fun of giving a small kingdom on a cube to somehow deal with if the campaign continues afterwards.

Definitely a good idea.

That's a fair, I never really had issues with it, but I made the connection between tGMM and Dead Gods much more explicit to nudge the PCs in trying to figure out exactly why the Modrons marched so early. With all the various options we have, if we just get creative, we can keep the players motivated.

And that's why I'm posting this, I hadn't even thought tying the Doomguard to Kyuss. I was planning on giving faction motivations up until A Gathering of Winds to help keep the PCs motivated until they meet Manzorian and see Diamond Lake suffer at the hands of Kyuss's minions.

Clueless, if you want some more information, this is the  AoW website at Paizo: http://paizo.com/dungeon/products/issues/ageOfWorms; and this is the Age of Worms Overload, which gives some more detailed information about each adventure in its first section: http://paizo.com/dungeon/news/v5748eaic9jz

Okay for some more random thoughts.

Themes

I really think that one of the strongest themes we could pull through the adventure path would be the power of belief. It's both Planescapey and easy can be added to the campaign without major adjustment. I've got a few ideas for sub-themes, but I'd like to kick them around in my head a little bit longer first.

Diamond Lake

As I said before, I think the hinderlands would be good location for the town. I was thinking that it could have a habit of drifting around the inner edge of the hinderlands close to the Gatetown. The Lake itself is nver far from the town. It changes positions from time to time, but it never leaves. This is actually the collective belief of the town in action, they just don't know it. They are all convinced that the Lake and the town will always stay together, and because of that, they do. The Spirewards end of the lake seems to collect graves, tombs and cairns of all kinds. This is due to the powerful magic that the Wind Dukes placed on the Whispering Cairn to make it remain with the lake and always commemerate the fall of Zosiel at the hands of the agents of chaos.