Have you tried running Falkenrath Aristocrat over Olivia? I am using Olivia for Commander but I tried her and cut her in my Vampire builds. Do you often get to use her abilities at FNM's?
No I didn't try Falkenrath Aristocrat , but Olivia Voldaren is very handy once she's out there :) (seeing that there are only 2 Olivia's in this deck she doesn't get out a lot...small odds to get her and it's a fast deck)!
It's a fast deck so usually it's over quite fast. If the game takes longer, I've got more chance to get Olivia Voldaren on the battlefield. Seeing that it's a longer game, I also have more mana on the battlefield (and probably an empty hand by then) so I get to use her abilities as well then. If I only use her first ability she get's big really fast (burning the small guys while doing that). I use her second ability just to take over the bigger guys.
Thanks for the suggestion but Olivia Voldaren has been a lifesaver in quite a few games so I'll keep her in here :).