The current standard reward for turning in herbs to the old man is a herbal bland. However, itd be nice to get a skill boost in herblore, or have the old man teach the character some herb knowledge.
For instance, I'm sure many players have gathered random herbs unknown to the character, and turn them in to the quest giver in the hopes that it is correct. However, even after turning them in, the character still doesnt know what the leaves are. Itd be nice for the old man to depart some knowledge about the herbs unto the character, or maybe even tell the character what the herbs are and where they can be found when the quest is given.