I thought about it a bit, but I actually thought of the Fire Sphere spell as something akin to a weapon; you display for a consistent combat check boost, and you can bump up the boost but it goes away.
It is not quite the same as a weapon. A weapon is a reveal (show it and put it back in your hand) to use its power with possible discards for additional powers. This spell is display (show it and place it on the table which is out of your hand) to use its power. While displayed you can continue to use its power. Discard activates another power.
I am in the camp that if you discard it for the extra d6, you do not get to recharge it. I do not see why this is such a contensious issue. The spell works differently than other spells. I expect that the game designers are playing with the design space to provide more variety.