[K]

The key thing to remember about vampires is that their only really good trait is their Immortality.

Sure, they have decent stats, regen, and an AP lifedrain attack, but they fail in the armor and defenses area and the "kill masses of dudes" area.

This means that you actually have an incentive to Empower them. Empower one vampire with Nature 1 for 50 gems and every army will have an immortal who casts Mass Protection or Wooden Warriors (though a dot of Earth is even better for Marble Warriors and Army of Lead). Give a vampire some Astral and just Magic Duel him all the time. He may lose, but he won't die.

Throw down Sabbaths with the freedom of knowing you don't care if the fatigue will kill the Slaves. Hell Power up knowing that Horrors coming to call is not necessarily a bad thing.

Heck, with a single dot of Empowerment and a Sabbath/Communion you can just spread self-buffs through the Communion and let the vampires go to town. A single dot of a path and the effect of a Communion and you could get things like Invulnerability, Soul Vortex, Astral Shield, Fire Shield, Quicken Self, Mistform, or Personal Regeneration.