It's a good thing that Freya (Rachel ) won the tournament by the way, because she gets a much better prize than Zidane does at that point in the game. I think she got the Coral Ring but Zidane only got money so it's much better to have her win anyway and it doesn't change anything in the storyline. As for the question about cards, well I never play it since I don't like it so I'm not sure if there's decent prizes to be won, but later on in the game you have to play during the plot to continue so it's probably good to get some experience in it