You can fix thurgadin faction literally in a day by killing Harthuks. If you collect their horns, you can even be smart and dump like 4 stacks at a time whenever your factzion drops to dubiously for instant ally again.
nah its really easy, and if you get bored with harthuks i believe killing the dragons in GD also increase your faction but im not 100% sure on that.
*EDIT:* you also get some gold and a bloodstone for everyhorn? or maybe just a bloodstone? i dont rememeber. but you'll get a lil bit of cash from it aswell
It will increase your faction with the dwarves, but it will destroy your faction with dragons. You need that dragon faction to do the quest. Repairing that takes a LOT longer. Don't kill the wyrms or drakes if you're doing Ytrazliarch. You need at least amiable faction for part of the quest.