mellored
Legend
This part doesn't have much to do with concentration directly. People always take the Shield spell or use their 3rd level slot on fireball.There are interesting spells no one ever takes because they aren't worth the concentration cost.
So... maybe have a penalty for casting the same spell over and over again?
Like...
Wizards can prepare more spells, but it becomes unprepared after casting.
Or wild magic sorcerer gets a random prepared spell each time they cast.