There were no oak wands or willows in DD. Staves are melee weapons; neither game required or used them for spell casting.
Crossbows can not be sharpened because they are ranged weapons. Realistically, it would have to be the arrows that could be sharpened. Converting normal arrows to power arrows has pretty much the same effect (piercing damage of normal arrows is 5-12, while power arrows do 42-90).
Willows are spiritual based weapons, and the damage is not dependent on how pointy they are.
Ok, for the first part, the staves are used for spell casting in Diablo, not in DD, which I think is more reasonable(what are mages if they don't have staves or wands, huh?).
While by "sharpen" we should not only mean "make the weapon pointy", we should mean "enhance", so that we can change a normal bow/crossbow into a power bow/crowssbow. No matter how pointy a pan is, it can never reach the quality of a normal sword by commonsense, right? But in BD, pans can be sharpened while willows and bows/crossbows cannot be enhanced, this is very weird. By craftmanship, surely we can convert a normal willow into a magically powerful super weapon, cannot we?
The idea of converting arrows is tipically on the wrong end. The damage of an arrow should be based on the bow/crossbow apart from their fire/water/earth/etc properties. The more powerful the bow/crossbow is, the more damage the arrow will do, doesn't this sound more reasonable?