Gale detonating the orb in act three doesn't explain why everyone gets cured of the tadpole (and partial illithid transformation), when Gale detonating the orb in act two causes everyone to turn into mind flayers. Considering his quest book talks about three items of Karsus: orb, crown and scepter, I'd guess that originally these were supposed to be combined into some powerful magical item. And Gale's quest was about getting the orb out of his chest.
I have wondered if the sceptre was originally intended to be the staff which you can find in the House of Hope. From the description in the annals it sounds like you would need all three objects to use them for the intended purpose, so Raphael only wanting one seems a little odd. If he instead had already owned the sceptre and then offered to take Gale's orb out in exchange for the Crown it would have offered a much rounder picture.
