What are your thoughts regarding a dedicated spell focus?
The inspiration for this idea came from the Dresden Files. Harry has a focus for his shield spell, one for fire spells, one for wind spells and one for navigating the Nevernever. He can cast the spells without his foci, but using them gives more control.
A dedicated focus for all evocation spells could grant a +1 bonus to spell attack rolls and damage, similar to a +1 melee weapon. Or a dedicated focus for all enchantment spells might add +1 to the spell save DC.
For a +2 bonus the focus might have to be more specific, i.e., only for fire spells or only for Wisdom spell saves. A +3 bonus might target a particular spell, i.e., only works for Scorching Ray or only works for Charm Person.
It could be magic treasure, but I also like the idea that an arcane focus should be created by and specific to the caster.
Just as a fighter can have a +2 sword, +1 bow, +3 shield and +1 armor, with this idea a spell caster could have a +2 fire focus, +1 enchantment focus, +3 Charm Person focus and a +1 illusion focus.
This doesn't seem unbalanced to me, but I am new to 5e so any suggestions/refinements/cautions will be appreciated.