RAI probably is "you can't use an edge point twice on a roll, and you can't use edge twice when splitting either". So no using Edge for extra dice, then to negate a glitch on the roll, no extra dice + reroll, no adding extra dice to each attack when performing multiple. If one argues spellcasting roll and drain roll can only take 1 edge, we get the same for dodging+resisting, screwing up a grenade throw and worse. That opens a shitcan of players looking at you and then walking away from the table, when you get them killed with this.
Carz: The problem would be opponents, not PCs, not coming default with SnS. And nobody cares about a Force 7, people care about players oversummoning Force 14 spirits.