I'm all for rewarding any behavior that makes the game more fun for everyone, but I don't think XP rewards are necessarily the best way to handle it. I'm of the opinion that a game like D&D runs best when all the PCs are at the same power level, so anything that could lead to some characters gaining levels at a different rate than others (3e item creation rules, I'm looking at you, too) has potentially negative effects.
In D&D 3e and 4e, however, there's a more immediate, less unbalancing game resource that would make great reward currency: The action point. In D&D 3.5 (well, in the Eberron setting, anyway), action points were spent to give a semi-scaling bonus on a d20 roll. In D&D 4e, they're spent to grant an additional action on one's turn. Either way, they're a potent reward that's still far from overpowering.