I would suggest Swiftfoot Boots over Lightning Greaves if you are going to be casting enchantments on your vampires. However, the 0 equip cost of Lightning Greaves is very nice for freely giving you guys haste. Ultimately its a personal call on that one. I would also recommend Terminate over Feast of Blood. Its an instant and prevents regeneration. I used to run feast in my vamp deck, but terminate is almost strictly better, save for the 4 life gain. Basically, you are trading instant speed and anti-regeneration simply for 4 life. I'd also remove Dark Impostor. Its a 3 drop 2/2 that does nothing else until you can get 6 mana. It is also way too easy to remove. I'd recommend Captivating Vampire over it. He's far more versatile, and lets you get more value out of your other vamps. He also kinda has a removal ability that costs no mana and also puts the removed creature on your side. Frankly, neither of those two removal abilities are that great, but if you really want something like that, captivating vampire is much better. I'd run at least 3 of him if you do put him in your deck. Whip of Erebos might be better for life gain in this deck than Eternal Thirst and it allows you one final swing with each creature that is already dead in your graveyard. (Great against control decks.) If you are running Eternal Thirst mainly for its other ability, i'd recommend Blade of the Bloodchief. Its much better, and since its an equipment, you can move it around between your creatures, unlike thirst.
Since it says this deck is supposed to be modern, I would suggest that you remove Bloodfell Caves and Akoum Refuge, as you need to be fast in modern. Ill let you mess around with the mana base on your own, but I do strongly recommend Cavern of Souls. Its a card that is tailored for tribal decks. Finally, put Vampire Nighthawk up to 4 as its just an amazing card. Some other cool cards to check out are Vampire Nocturnus, Gatekeeper of Malakir, Anowon, the Ruin Sage. All in all, not bad and I like your sub-theme of burn with vampires.

Also, forgot to mention that you have two cards in your deck that aren't modern legal- Blazing Salvo and Tyrant's Choice. Lightning Bolt would make a suitable substitute for salvo.

Still prefer Lightning Greaves over Swiftfoot Boots, the 0 cost to equip is incredible. I was actually thinking about removing Dark Impostor, and then putting another Rakish Heir, but still don't know. Probably will take out Feast of Blood to put Terminate since it's disappointing to being unable to use it some times. Also, it's actually a good idea to take out those Eternal Thirst for some Whip of Erebos, I'm just not so sure about the mana cost, but will try it out a little. Thanks for the suggestions!

Needs more Blade of the Bloodchief.

I like.

Look at mine if you want Plumpires. I didn't knew or paid attention so similar ideas with the Stromkirk Captain. Fantastic deck! Mega! I voted for it.Look at mine decks if you like. They're all Modern Ideas.

You should probably add Olivia, Mobilized for War considering it grants the madness a lot more and it make Olivia Voldaren a lot more useful allowing you to add more than just vampires to the deck such as Mad Prophet and so on.

Otherwise it's a great deck. I love vampires and made my own deck "Vampire's Rule!"-Olivia Voldaren you should check it out.