Fight effects are like, just a single mana even with their most recent versions, and Im pretty sure adding a +1/+1 counter doesnt warrant multiplying its cost five-fold
They do give you access to some otherwise non-viable cards that are pretty potent in the archetype
Magic: the Gathering - Fog (172) - Magic 2013
Each activation improves card quality or advances mana development, which gradually pulls the deck ahead without forcing risky plays
For example, the game has a Slowpoke card with its original Base Set artwork, and then a full-art variant that removes the frame to reveal lots of other Slowpoke crawling all over the card in humorous fashion
If you stick solely to Vampire Aristocrats like the precon promotes then I think Clavileno and Carmen are about the same power level where it boils down your own preferences and your own meta: Clavileno is cheaper and provides a slow but consistent payoff, whereas Carmen is more expensive but also more explosive and randomly becomes more powerful if you happen to play against decks that sacrifice a lot (fetchlands, treasures, other Aristocrats etc.)