Vampire skill cost decrease and cost increase should be tied on the amount of vampire skills slotted.
Cost increase on non vamp skills(also ultimates)
>1/2/3/4 %
Cost decrease on Vampire skills;
>2/4/6/8 %
Fire weakness and health reg reduce should stay as it is, maybe increase fire weakness to 25% on stage 4.
You only want to use the juicy stun on your magcro then stay stage 1 (u still will be suffer 25% health reg loss, 5% more fire dmg, 1% cost increase on all skills incl ultimate ) and be this weakly thin blood.
Or you will be the great big bad vamp lord. Stay stage 4,slot all vamp skills turn every 15 second in a big bad blood scion and and run away through the shadows WITH All strengths and weaknesses a vampire lord will have.
Or you find the passives only interesting, a vampire 4 you is a race not a class? U want only the undeath passiv for your build? Then you have to sacrifice 75% reduced health reg and 15% more fire dmg for it.
Or be whatever is between those choices.
That is my definition of a "play as you want" and the vampire will be such more flexible for everyone. Average Joe can role play as vamp through Overland, Pro gamer Kevin can min/max all day to find the perfect sweet spot.