I would say it's dependent on the game, and style of play. For my game, it will add a bit of fun to it, and, like you said, add time to the gameplay. However, I'm not letting people level off of it, as it will only give +1 exp point when you craft something. So unless you craft an ungodly amount, you won't gain all too much from it. So yeah, it boils down really into:
1. How do you plan to use it?
and
2. Are you going to allow them to level off of it? If so, how much?