The problem isn't the value of the key, the problem is how SteamGifts system works. If you win a giveaway, you are expected to add said game to your account. Not having that game to your account flags you (the winner, not the giveaway creator) as not activating your wins, which can lead to your account being banned. I have had that happen with a game that provided the gold edition key instead of the base edition, since those were considered by Steam as different app ids.