5e is balanced around hitting roughly 65% of the time (8 on a d20) for all levels of play (assuming no magic items or Advantage). 2d4 Bless is on average a +5 bonus, meaning that characters will now hit on a 3 or better = hit 90% of the time. That's pretty powerful.
That staff [of arcane blessing] is amazing imo. It doubles the attack and saving throw bonus of Bless from 1d4 to 2d4. Plus it gives Blessed casters +2d4 spell attack as well(Bless doesn't affect spell attack). So with the charge on the staff(no cleric needed) once per long rest you can have anyone you want uber Bless 3 party members for a fight.
Also wait, why doesn't Bless affect spell attack? It totally should. Bless should affect all attacks - melee, ranged, or spell.
