My evaluation is that Player Side Quests are generally not worth the effort. The problem is they cost you at least a whole turn of questing, with the encounter cards that entails, which is a high cost. The effect here is definitely welcome, especially in a game with more players and/or a quest with many enemies. You do want a way to grab it, since it's much stronger early and you don't want to play 3 copies since number 2&3 are dead cards. So Dúnedain Message, Thurindir or The Road Goes Ever On are close to essential. All that effort, you'll probably get more use from Captain of Gondor or Dúnedain Warning.
Player Side Quest. Cost: 1. Victory 1.
Limit 1 copy of Keep Watch in the victory display.
While Keep Watch is in the victory display, each non-unique enemy engaged with a player gets -1 .
"I called for the help of the Dúnedain, and their watch was doubled..." -Gandalf, The Fellowship of the Ring
Alvaro Calvo Escudero
Beneath the Sands #59. Tactics.