You've saved Twilight and your friends, including many, many ponies at the Equestia Games, manby times. And plus, your the Prince of Friendship along with the Princesses of Friendship! You're awesome, Spike!
Let me count the ways why Spike matters: 1. He SAVED the entire Crystal Empire 2. HE brought Princess Celestia when Twilight was melting down about not learning any friendship lessons 3. He made Twilight get back up and fix her friends when their cutey marks got messed up. 4. No one could be a better friend than Spike. (Plus he's adorable ^3^)
Spike IS important. And no one should forget that.