They honestly don't visit so much where it's annoying or infringing. Same with aliens from GTW. Abductions are kinda rare. Not as rare as Vampire attacks but they only happen here and there.
Sims just pass out when they're bitten. They don't change into a vampire at all unless your Sim asks them too and they get an uncomfortable moodlet for awhile 24 hrs I think? You can lock your doors and the vampires can't really gain any entry (less they have that power, but I have yet to see them forcibly come through locked doors). All they lose in a loss of good nights sleep rather than their lives.
You'll definitely see a lot of 'fake' vampires walking about at night in some pretty weird outfits. Like some edgy sims wanting to wear goth related items. The CAS and build/buy items are great. The cobwebs and cracks you can place on the walls are very nice, especially if you want to make sims have run down homes.
If your Sim is up past a certain time sometimes you might see one lingering outside your home, but they won't break in less you're asleep. If they DO break in and you're able to get your sim up to wake up they won't attack. I tend to shoo them away and lock the door if I forgot about it.
Plus there's coffin and bat woohoo~ :p