So I broke down and bought Zombie Dice Two: Double Feature. It really is a very cool expansion of the game. It's so worth the 8 bucks.
The new dice (you swap out standard yellow or green dice to keep 13 as the total) add several fun twists and the one I didn't expect is that the two 'hero' dice, if rolled at the same time, can "rescue" each other. The Santa die (yes) can power up your Zombie (helmet = tough, you take 4 shotgun blasts to kill, not three, or Energy Drink gives your Zombie extra speed so all the rolls of Feet are treated as Braaaains... NICE). Of course, Santa may still blow your head off... if you've been naughty, I suppose.
So I'd say it's totally worth it. More yummy brains, more fun!
Here's the rule sheet (link from www.sjgames.com)
Speaking of fun with Zombie Dice, dig this.