I think a Spirit Guide for every color would just be cool, to allow decks of all colors access to minor acceleration. Many different decks can benefit from them, especially stompy decks. Giving combo a few extra tools hardly seems like a big deal, considering that they aren't dominating or warping the format right now.

Voracius vampire RB
Creature - Vampire
Haste Fly.
At end of your turn you lose 2 life.
4/1
Goblin Escort
1R
Creature - Goblin Scout
Haste
Whenever Goblin Escort attacks, defending player reveals the top card of his or her library. If it's a land card, that player puts it into his or her hand.
4/1