Some thoughts:
The big narrative concept is that Goblin Magic interrupts your action to provide more information, which you can act on immediately.
The L&F model says that Goblin Magic happens when at least one dice rolls your Magic Number.
If dice which roll your Magic Number don't get re-rolled, your total number of possible successes is reduced for the action informed by Goblin magic, and that's not very magical.
If you only re-roll the Magic Number dice, then your revised action is informed not only by your insight from Goblin Magic but also by knowing how many successes and failures yo…