Tony Vargas
Legend
You could tweak a few spells to make them more dangerous. The classic fireball & lightning-bolt, for instance, could easily hit a different area than you had in mind. 5e's TotM doesn't lend itself to mapping out the cubic footage of a room & surrounding corridors or the angle of incidence at which a lightning bolt rebounds or anything, but, you could do something simpler. For instance, you could base the AE in feet of damaging spells on the damage roll, so the bigger the damage, the bigger the area. You could require an attack roll to target a spell precisely. You could replace the Evoker's ability to edit allies out of it's AE with Disadvantage on enemies' saves when there is an ally within the AE and adjacent to them...
Or, you could add new 'Name' spells to the Wizard's list, that are flatly better than similar spells of the same level - they're just very hard to find and risky to cast. So Päirömöinen's Ball of Abysmal Flame is a bigger, deadlier fireball, but whenever you cast it, you have to save vs the same DC, yourself or bust into flames (half damage).
I can see that you're trying to make daily spells higher-impact, but you might want to think about whether you want to do this for NPC/Monster casters. Though they may have nominally 'daily' spells, as adversaries of the party, management of that theoretical daily resource will rarely matter - because, y'know, they'll either wipe the party or die. Unless you have a recurring caster villain who's spells aren't going go re-charge between appearances, you might want to stick with the standard rules for them.
