The purpose to the Healer / Herb Quests is not for instant xp/reward they are intended as background quests you can take or complete while you explore the lands of Myzan. Herbs like Crystals spawn randomly on one type of terrain, in this case grass finding a specific herb is not that easy, so it is better to pick up all the herbs you find while in the process of moving around between dungeons , towns, trainers and buildings and then check the quests a healer has when you are next in town to see if you can complete any. You can also check the Marketeer to see if another player is selling one, Crimelords get a Track Items skill which can be used to find already spawned Herbs and therefore makes a nice skill to have at later levels.