Taking the Krand of the Bloodreaver letter a bit further and realizing that my characters really seem to like having physical copies of letters and such, I've created a back story that the creatures in the Nentir Vale are loosly banding together to try and take down all the human settlements.
I ran Kobold Hall and had the players overhear a conversation between Kalarel and Szarthrrax about the dragon being the ring leader toward getting this done and Kalarel giving him some treasure and artifacts to get some sort of magical artifact from the dragon (something to open the rift, but that wasn't made clear to the players).
In the absence of the dragon, it appears that Balgron the Fat is working with some to funnel the money. As a result, he's not quite as trusted by Kalarel which is why the second level is sealed and passworded (explanation altered in Ninarin's letter). In addition, the characters found a letter explaining the plan signed by one of the mages of Saruun - returning the Nentir Vale to the creatures and then pillaging the cities for magical artifacts that would extend the mages rule over the city. (Little do they know now that it really isn't one of the mages secretly trying to assert control, but Paldemar with the hopes of also framing one of them and causing a massive distraction while he's able to complete his task in H2)
In addition, another found letter later revealed some key names about thunderspire - like the druegar clan, the gnoll blacktooth clan which is sending raids out in eastern nentir, etc. On their second arrival to the keep to push into the second level, they found blood train back again to the torture chamber. A very quick fight and they find the priest from Winterhaven trapped. Apparently she was out doing her own cult research when the Bloodreavers captured her. She thanked the players and went off to town to warn them of something she overheard - a big attack on the town trying to raid them and weaken their resolve. The players chose to let her and the militia deal with that and push in to stop Kalarel.
Overall there's lots of clues and ideas about heading to Thunderspire - the source of all the evil currently. I'm also digging the setup as the player talk seems to really think this Mage of Saruun is pretty evil and should make for some good roleplaying in H2 should they try and out him or confront him. Some of the links I've created in the letters I wrote should also give the feeling that there are several benefactors and people behind the various attacks (one with links to kobolds, one with links to the goblins, etc) in the seven pillared hall that should eliminate the "princess in another castle" as they feel they need to go take care of everybody to save Nentir Vale.