if the differences I'm seeing in the mood of the book are intentional or are artifact of the revisions.

Before reading this thread I was going to start a new one about the stark differences in mood between volume 1 and what we're reading now. It hit me when I went looking for LOL lines in this section in response to another thread; I had a hard time finding them! I was thinking that the shift helps to emphasize the differences in location, with their attendant differences in attitude. Bath is a vacation spot, designed solely for enjoyment, and there even the duplicitous villains (read: Thorpes) are lively and entertaining. Northanger is an Abbey, with a history of solitude and monasticism, so it would seem that its duplicitous villain should be more solemn and scary, in line with what Catherine has read about ("It was the air and attitude of a Montoni!").