Strictly speaking in terms of action economy, I think it would probably "feel" better for a spell that takes twice as long to cast being more like 2.5x as powerful as opposed to 2X as powerful, because players generally don't like to spend their turn doing "nothing", even if it's clearly in service of doing something powerful the next turn, but I'd have to experiment with it more to know for real.[/FONT]
In 13A the sorcerer also gets a random chaos effect on the round they lose to gather power. It's either some kind of small but automatic damage to nearby enemies or a bonus to your defenses until your next turn starts. I know the sorcerer in my group typically has zero problems making that trade off and uses gather power whenever they can.