If you look at a Scepter in-game with maxed WIS, your damage number will look something like
Damage: (X+Y) (+Y)
I think it would make sense to implement the damage of your weapon on the weapon’s stats like how WIS-mod has changed abilities to display their altered value for healing, bonus health or damage. You can also always just subtract your (+Y) value to get the original damage of your weapon.
Example:
Scepter of Devastation
Damage: 
This is a Scepter of Devastation with 66 WIS. It gains +160 damage on top of its base damage of 820, which makes it deal 980 damage.
Tier 12 Wand
Damage: { (0.5 + ATK/50) × Weapon base damage
This is a Winter’s Breath Wand with 70 ATK. It gains +85 - 126 damage on top of its base damage of 95 - 140, which makes it deal 180 - 266 damage. If I can make a forum post and do it, and if WIS-mod can do it, I don’t see why this shouldn’t be a feature for weapons aswell.
Please note that, if you are unfamiliar with the formula for calculating the damage values of a weapon, it can yield a negative modifier if your ATK is low enough. For example, at 10 ATK, your modifier becomes ×0.7, 30% less than the base damage values. Instead of being 95 - 140 (base) it would be 66 - 98 (-29 - 42).