All true. That staff is one of the main reasons I choose the -cast casting build over the others.
The +2 casting time staff is useful in a lot more ways than curing. It works for every light magic spell(including songs if you're a brd). Rushing in to cast Protectra ,Shellra, and auspice mid-fight, status removal spells, regen, raise/reraise, light dmg spells... it all goes by noticeably faster. The sigel sash plays a part as well.
Its a good staff and is definitely worth it.
Now that its possible to swap between the potency staff and the +2 casting time staff, I might start doing that.