I cannot think of any quest that involves a sack of grain, so if you have got all the crystals I would tend to ignore it.
As for starting over, if the PS version is like the PC version, then you have the chance to play through some of the other quests and get your character to a high enough level to take on Draak. Honestly, it's not a failure if you cannot kill him after your first runthrough. For example look at
this screenshot from WZ's site. In it he is level 54, but has not killed Draak even once lol
Keep playing and have fun