I have one simple improvement for magic users of all stripes that doesn't involve dice throws. It is a clarification of my house rules.
First - To loose and/or lose a spell it has to be prepared. This is usually part of the rules of the game. One word to improve this rule is "completely", as in "completely prepared".
Adding this one word completely changes the dynamic of spellcasting.
Let's say a wizard or cleric selected a complex spell. They start to prep it then they are hit in the face. "Completely prepared" switches the result from "I lost a spell" to "I have to start over". They weren't done prepping. That seems kind of fair as the player and the character pays a cost in terms of frustration but doesn't actually lose anything else.
They need a better plan, but they can use that spell later.
The next modification to spell casting for simplification is: to allow the character to pull back unused spells. I can't tell you how many times I have had a player prep a fireball in the last round of combat and simply lose it. It seems reasonable to me that a player should be able to undo that action if nothing else is happening. Perhaps it takes the same amount of time to put the spell away as it does to prep it. Seems reasonable to me.
A third simplification is what I call "spell coast". On Monday, a cleric prays for three spells - Light, Purify Food and Water, and Bless. He has only one opportunity to cast the Purify Food and Water spell on Monday. On Tuesday, decides to replace that one spell with Cure Light Wounds. Being a small-town adventure, nothing happens until Sunday night. If the cleric is happy with his spell choices, he doesn't have to study every day. He coasts along with the 2 spells he prayed for on Monday and third, he prayed for on Tuesday.
The less time the players spend memorizing spells, the better. I had a diabolical DM that would take people's memorized spells away the moment they lost consciousness.
All of these things together make spell casters more powerful while also providing more role-play opportunities.