Here is my idea, but wizards need more than just this.
Change kill-nuke talent to guarantee a mana reward of, arbitrarily 200%, 250%, mana cost of spell.
Give Wizards another line of nukes, make them very mana inefficient, but bigger damage than anything they have. make this the closer nuke. if they land it, it isnt mana inefficient at all, and is a bigger windfall back of mana because of the high cost.
This would increase their effective dps in fights in a logical way that is consistent with wizard identity (big hp chunk dmg). This would alleviate mana issues to a degree, especially in groups. This would reward an active playstyle and help make the class fun and give the wizard players the big numbers they want.
One big current problem is the wizard as a chunk dmg dealer does not really participate in the first 20% of the fight. Their predicted-dps doesnt really mean anything. It is a near useless calculation at the moment. Their real dps is how many nukes they have time to cast in the 80% of mob hp they are active, or how many they can afford to cast due to mana, divided by fight time. This gives them a really low actual dps value.
Giving them a big closer nuke that windfalls mana back would be a great risk/reward move to help.