You should probably lower the fertility still further - a lusty couple can still reproduce with a -10 fertility modifier. Being a vampire should definitely increase your intrigue considerably, and probably your diplomacy as well, but should probably give a mild hit to the other two.
You might consider tweaking some of the "I could be a better courtier" events to "I am ready for the kiss of the vampire!" events. You could also tweak some of the conversion-because-my-liege-is-a-different-religion events in that way.
You should probably modify most of the existing disease events to not fire if you are already a vampire. You might add some events making you corrupt and vicious over time because of your vampirism - some events that might get added include: wise, skeptical, heretic, cruel, chaste, excommunicated, selfish, madness, vengeful, deceitful, proud, suspicious. Certain religious events shouldn't fire if you're a vampire, like the "God will forgive your sins" ones. God will never forgive your sins; He has forsaken you.
You could add a random event to possibly slay the ruler if you have a valorous and zealous courtier - possibly give a choice between a) killing both characters, b) severely wounding the vampire and making him cowardly and stressed, and killing the courtier, or c) making the courtier the new ruler, giving him some stat boosts, and killing the vampire. A player would never pick option c unless the courtier was a relative, but the AI might...