Hmmm. Been thinking lately about a "casting" roll for spellcasters.
Right now, spells that require a save have after a fashion a casting roll built in - if the opponent makes the save, the spell fails. Those that require an attack roll fail if they don't hit the target.
However, spells that affect one's self or an ally traditionally don't require a roll of any sort, they automatically work. What if this wasn't so? What if casting spells such as bless or invisibility required a "casting check" - something along the lines of DC 8/10 + spell level? Certain circumstances could apply disadvantage (casting on the deck of a heaving ship) or advantage (a spell of your School specialty or Domain spells) to the roll.
Would it be significant? Would there be any knock-on effects (perhaps more slots, since spells can be failed)?
If this was used, should we change how saves are done? The opponent having static defenses like 4E and the caster has to roll to overcome them?