I like the concept of Trophies, but I don't think they're entirely necessary.
Trophies give me an incentive to finish of some of the side quests I wouldn't normally bother with. Often after I finish the main storyline of a game I often don't go on to do post-game stuff unless I really loved it. But, at the same time, I get really annoyed when I didn't finish a game (because it was awful) and have a really low trophy score on my a profile. So it's a mixed bag for me.