It is a good idea to do all the side quests. In addition to the experience, gold, and Rift Crystals you get as a reward, you also work towards the achievement/trophy:

The Hero
Completed all pre-planned, non-notice board quests.

An Uninvited Guest Walkthrough

The sidequest "An Uninvited Guest" takes place in Cassardis. Go to Pablos' Inn:

Pablos: I've got a favor to ask, if you've got the time to listen. It is a matter of warding the village for crime. (Choose to hear him out.)... A thief. He strikes the same spots each time. Heraldo's Grocery and Aestell'a Apothecracy have suffered, as I have. The rat steals at nights, and pinches the food and vital stores we've gathered for times of need. A skilled wretch too, and well crafty. There is a strict order to his thieving. I've spoken with the others and we've agreed upon a plan to catch our rat. They are none too pleased at this violation, and eager to get rid of it. Best you go and speak with them. Come and find me after, I will explain the plan.

This starts the quest:

An Uninvited Guest
Speak with the thief's victims

Objective
The fisherfolk of Cassardis have a thief in their midst. Help Pablos catch the Scoundrel

Details
Talk to Aestella and Heraldo

Go south to Aestella's and Heraldo's shops and speak with them. Then, go back to the Inn and talk to Pablos who explains the plan. Tell him you are ready. The game will skip to night time. Exit the Inn, and locate the thief who should be running on the streets. Give chase.  When you catch up with the thief, GRAB him (don't kill him). Pablos thanks you for a job well done. This completes the quest, An Uninvited Guest.

Lost Faith Walkthrough

Talk to Father Clemente at the Cassardis church, (Village Chapel, south side of town) who has a favor to ask you. In the wake of the dragon's coming, many of the villagers have come to offer prayers. But Clemente's Scriptures are missing, and he has yet to commit the verses to memory. Without the text, he cannot offer up proper prayer. The scriptures were secure in the chapel the last time he saw them. He does not wish to believe them stolen.

This begins the quest:

Lost Faith
Search for the Scriptures

Objectives
Father Clemente misplaced his scriptures and has great need of them. They must be reclaimed at once

Details
Seek Father's Clemente's missing book. Like as not, it remains in the village.

Open the map and locate  the red marker. You have to climb onto the walls to the north, then jump landing on the red rooftops, and walk to the location of the Scriptures. Then, you have to return the Scripture to Father Clemente. Open your inventory, and hand over the Scriptures to Clemente.

This completes the quest, Lost Faith.