I was recently playing against an opponent who claimed that he could trigger Wampa's ability to cancel his die results after dice and tokens were spent and results were compared. To me it seems that his ability would kick in during the "Modify Attack Dice" step- in particular where "the attacker can resolve any card abilities that allow him to modify attack dice and that he has not already resolved during this attack".
I just want to be sure he was doing this correctly. I lost two of my three ships to him waiting to see what the final results were before scooping up his dice and saying "take a face down card". This seems rather extreme if this was being played correctly...