Use treasure cards wisely. Don't use one when you have a card you can use just as easily and that will do what you need it to do in your deck. Treasure cards come in really handy because they can let you use spells that aren't in your deck. Even if it's the same as a card you have in your deck, treasure cards effects are amplified. Attack cards do more base damage, blades and traps amplify damage more, shields protect against a higher percentage of damage, and healing cards give you more life. Also, since your sideboard is smaller than your deck, you can use them in a pinch if your deck doesn't cooperate with you and give you the card you need. All of these are great advantages. So, to prevent wizards from simply using treasure cards and ignoring their actual school spells, treasure cards are single use cards. You can still rely heavily on treasure cards if you want, but it means you're going to be spending a lot of gold to keep your supply of treasure cards up. You also might not always be able to find some of the treasure cards you'd like to buy. So, when it comes to the harder to find cards, use them only when you need to, or you might not have them when you really do need them.
