don't ever sell your cards or give it to someone that don't take care of them, and don't be the mother that says that you musst give them to your little brother despite him being a total dumbass
Buying the best cards is basically like using a command in your survival minecraft world.
You'll get a moment of satisfaction but you'll quickly grow bored of your world soon enough. Since you've done it once you'll not feel like wasting time grinding again and end up cheating again and again. Soon the world will lose its position of being built ground up by you and you'll lose interest in it.