First let me start off by saying I read your initial question but none of the responses so I'm sorry if this is redundant.
I am currently running RotR and my group just finished burnt offerings.
I had my group describe in detail why they came to Sandpoint on this particular day, and how they went about it. (Only had 3 players, two of which were in-game traveling brothers) and that alone added about 3 hours of game time before the festival even began. This helped the players get introduced to some of the NPCs, the layout of the town, and ultimately improved their connection to the town. Once the festival began the next day, I wrote out things to do at the festival (it gives a brief idea of what goes on) and wrote out speeches for when the notable NPCs took the stage. My players told me that it did in fact improve the quality of the assault, and made it more fun to play.
As for shops and stuff, I make them roleplay buying things and that also introduces them to the world and builds connections.