I'm actually in the process of piecing together a vampire tribal deck myself. (You can see the list at: http://deckbox.org/sets/279257). Admittedly mine is a bit more expensive than what you're running here... but not too many of the big pieces are absolutely necessary. You're welcome to take or leave any of my thoughts there, but it might give you some ideas.
To start off, I agree with everything HikingStick is suggesting. The captains are essential and should be a 4x. More burn would definitely be a welcome sight.
Now for some more pointed suggestions.
First, while it might not fit the tribal theme, I would suggest some sort of a one-drop. I know you're going for casual play but I cannot stress enough how useful that first turn play is. Even something like Rakdos Cackler immediately puts the onus on your opponent to respond. Obviously the ideal one-drop for a vampire deck would be Stromkirk Noble but a playset of those will run you roughly $10 while the Cacklers will likely run you $0.50.
Second, one card you should DEFINITELY spend the 50 cents to get two of is Rogue's Passage. As I'm sure you're aware, this deck will sink or swim based on whether you're able to actually land some hits on your opponent early game to make the vampires grow. Without those hits, well, none of the vampires are all that threatening on their own. The passage will make them unblockable to guarantee they will grow (especially with one or two Rakish Heirs in play to compound the growing effects).
Third, if you're going for flavor, I would suggest tossing in Bump in the Night and/or Exquisite Blood. The former lets you smack the opponent for three early and possibly another three later in the game (which can often be a game breaker). Exquisite Blood can be a monster as it almost gives all your creatures lifelink (not quite, but about as close to as you're going to get here). Another option would be Mark of the Vampire - why not pump and give lifelink? That alone can be a game winner in the right circumstances.
Fourth, while I know triggering Falkenrath Noble was a perk to Bone Splinters, most of the time you really won't want to sack your board presence, especially if your position will improve with a free swing as much as it will (given the vampire +1/+1 counters). Thus, I would suggest Tragic Slip, Victim of Night, Ultimate Price, or even Brimstone Volley. You'll be killing THEIR creatures without costing your own. Not as many triggers for the noble, but still, more creatures on your side will work in your favor.
Lastly, I can see where Sign in Blood needs to be in here. The last thing any deck wants is to be topdecking, thus, any added drawing can decide the game. Sure you lose two life, but that's a single hit from a Vampire Nighthawk to replace.
Anyway, best of luck to you with it.