I absolutely love the idea behind this deck, politics in EDH is one of the most underappreciated parts of the format, and Black is so rarely considered in terms of it's political value. I don't think that once-off buffs like
Rush of Vitality are where you want to be in an EDH deck; they seldom really impact the board in a very meaningful way unless your deck is built around utilising them to their fullest potential, in some sort of Voltron strategy. As for what to put in instead, I'd agree that Gonti is a big one- he lets you utilise your opponents decks to your advantage, and creates a really interesting boardstate when you have any mana untapped (although that being said, I think he'd fit better as one of the 99 into the deck when you have very little ramp focus in it's current iteration). Other cards worth considering are
In Garruk's Wake for a 1-sided blowout, and the 'turn control' cards.
Mindslaver, Emrakul and
Sorin Markov are incredible bargaining chips in a political game, and things like
Cruel Entertainment serve to really shake up the board.