Someting that I bear in mind is that the Vampires available as player characters aren't full vampires, and while they don't have all the strengths of a full vampire they are more than compensated by lacking the weaknesses - and they can gain some of the powers by purchasing the appropriate talents.
The Con issue... is a bit more difficult. If you are rolling dice then roll Con as normal, but it becomes - at nightfall. (This is what I think was intended.)
For point buy... it depends. I have allowed people to ignore the trait when creating their character, but when they are mortal by day they have either a 6 or an 8 Con (I have tried both, and prefer the 6, my players prefer the 8...)
Or you can say that if they do not spend points on Con then they are dead by day, unable to move at all, and entirely vulnerable to the nice doctor with the stakes and the mallet. If I were to add the vulnerabilities to crosses, running water, consecrated ground, and holy water these would be the ones I would pick on, the ones who are dead by day, they have severed ties to their mortal selves. A wise player will put at least a few points into Con.
The idea of vampires being destroyed by daylight began with the movie Nosferatu - and Dracula had no trouble with daylight at all.
A stake through the heart while helpless will kill just about anybody, let alone vampires, as for doing it on the run so to speak... contrary to what you might think from watching Buffy vampires do not have rib cages made out of sponge cake, you need to hold them down (while he is almost certainly in undead rage) and hammer the stake home, breaking ribs as you go. Messy, and not all that easy.
I do not allow 'staking with arrows', the rules for mortal characters do not allow for it, why would a vampire be more vulnerable? And as I said, an arrow through the heart would kill just about anybody. And like the daylight vulnerability the vampire coming back once the stake is removed was created for the movies.
And for what it is worth - driving a stake through a fresh corpse will make it scream as air is forced out of its lungs, no undead state necessary for that one...:evil:
For those who want a semi-period book on vampire hunting look for Montague Summers' book The Vampire, His Kith and Kin... Summers was a self described Vampire hunter.
The Auld Grump
*EDIT* I think that both Hunters and Explorers should have Hide and Move Silently, I think leaving them out was an actual mistake, not an intentional decision...