This is a rather cheesy question about min-maxing.
Staffs in SoP work a little differently than plain Pathfinder ones. The enhancement bonus applies to CL of the sphere effect, and extra talents can be included in place of +1 bonus, much like how weapons and armor and their enchantments work.
The damage of your destructive blast increases by one die. You may take this talent an additional time at 5th caster level and every 5 caster levels thereafter; the effects stack.
Any caster wielding the staff gains access to a magic talent contained within the staff. If this talent is a (form) Conjuration talent, it may be applied to any companion the caster summons, but no more than one creature at any given time. To contain an advanced talent, a staff needs a minimum caster level equal to that talent’s prerequisite caster level, and must contain all of that talent’s prerequisite talents. A staff may gain this special quality multiple times.
You may aid another spellcaster who also possesses this feat, granting them a temporary +1 bonus to their caster level, as well as granting them access to your spell points and talents as if they possessed them. You must spend a standard action every round to maintain this ability, and you must be within 30 ft of the caster you are aiding in this manner.
A target may be aided by multiple casters at once in this manner, but all involved casters must remain within 30 ft of each other, and the effects are not strictly cumulative. It takes one aiding caster to add a +1 enhancement bonus, three to add a +2 bonus, six to add a +3 bonus, ten to add a +4 bonus, and fifteen to add a +5 bonus. No caster may receive more than a +5 bonus in this manner.
So if you had a +1 staff with greater blast (1) and a caster who had taken greater blast once, they should be dealing damage at 1d10 per die as the talents should stack. Two casters with circle casting should also stack due to this?