I'd suggest switching your Connoisseurs for Bloodthrone Vampire . Cheaper cost, biggest boost. Otherwise it's the same thing.

This is my mono-black vamps for M13 if you want to check it out. deck:sanguine-my-brother-m13. On another note, I'm not too keen on Screeching Bat  ^Flip . Plus you have 64 cards, you'll probably want to cut 4 out somewhere.

I don't see why splashing Red for a more powerful deck wouldn't be a solid option.

With red it brings Falkenrath Aristocrat , Olivia Voldaren and Stromkirk Captain and these will all still activate Vampire Nocturnus .

Also the return of Vampire Nighthawk he is going to be beast in vampires.

Cut the Nobles its blood artist except worse

if you are running red, you need Olivia Voldaren . i also think you have too many creatures and could use some more control or draw power. you can cut a nocturnus, the interlopers, the nobles, and a bloodline keeper. this can give you 2 olivia voldarens and 4 sign in bloods. duress would also be a good card to add as it can get rid of things that black cant typically get rid off before it enters play.

I think some humans with haste will help, more 2 drops less 3-4 drops. Ash Zealot or Rakdos Shred-Freak . Maybe sideboard some Pillar of Flame and Annihilating Fire .

That's the kind of thing I was looking into, I've got other suggestions for putting Blood Artists into the 2 drop slot, cutting some things and putting Rakdos Cacklers in for more early game board state.

if you have the budget i would drop a blademaster for an olivia, it triggers nocturnus and is immune to most removal in standard right now. drop a night hawk for a b-keeper, Blood Artist is a good choice, Rakdos Keyrune could help in here