Re: Roll the dice once - worth anything?
I don't see anything wrong with it. I think you just need to make sure the player accepts the results for both powers. He could roll really, really well for both. Or the 4 dice could roll really, really crappy for the one power.
It would save time. Maybe give the character a -1/4 or -1/2 lim for it. Just as something to seal the deal because I think some players wouldn't go for it.