I don't think the discovery of the plane was for Locke's benefit so much as it was to sow the seeds of conflict between him and the other survivors:
(SO MANY SPOILERS AHEAD)
- The drugs inside the plane (nearly?) led to Charlie relapsing (conflict with Charlie)
- Eko was deeply affected by discovering his brother's body, and spent a bunch of time building a church in his memory (conflict with Eko)
- Climbing into the plane killed Boone (conflict with Jack -- this leads to Locke finally telling the rest of the survivors about the Hatch)
You made it more clear that you're asking why was Locke pushed to find the Pearl, but I think it's pretty much the same explanation: The discovery of the Pearl station led to a pretty basic argument over whether pushing the button was "real" or not (and flipped Locke away from being the Man of Faith for a while). This conflict with Eko led to their showdown and the use of the fail-safe.