I prefer having Magical damage only scale with level stat and or skill proficiency instead of having the same exact mechanic as fighter.
First I think this is more immersive that casters don't rely on equipment to be efficient (they still need stat bonuses but don't rely on their weapon.), as opposed as Melee who always need to get the best weapon to be at their peak efficiency but chances are you won't change weapon every level so to me it balances out.
If you want a wizard scaling with weapon, you can dual wand (as it has been mentioned above poison+fire) to shred magical armor and then cast your awesome spells. But I am perfectly fine with casters not having spells scaling off weapons.
It also gives you flexibility to switch your wand or staff to different elemental attack without completely screwing your spell damages, because I doubt all your wand would be of equal strength.
Facing skeletons? Damn I have to remove my poison wand for a the fire one which 3 level lower, all your spells loosing effectiveness