Quest lines for certain items that are then "upgradable" or "modable" in future quests would be a good idea. What I mean is for example, is perhaps you get a helmet from the quest then in perhaps 4-6 levels you can start the next part of the quest that is there to "upgrade" the helmet, adding a few stats (perhaps even a way to let the player choose the way the item is upgraded... I.E Power (full DC/SC/MC) or Defence which obviously is as it sounds, would have more AC/AMC and perhaps even a "mix" option where the balance of the stats is not too much towards offense or defence.
These quests would have to be challenging with several different stages. A stage where you have to find something, a stage where you have to solve a riddle and find the location from the riddle, a stage where you have to overcome a powerful foe and finally an ingredient collection phase.