I think whether Vamps eat or drink has to do with the story being told. I don't recall Barn actually eating or drinking when he was a vampire, but did occasionally hold a drink or cup in his hand.
Vamps in the Buffyverse seem to still eat and drink whenever they want, but require blood for sustenance (Spike likes buffalo wings, and blooming onions, for example)
Chelsea Quinn Yarbro's Saint Germain, often demurred when around others were eating or drinking, usually claiming that he prefers to dine alone.
I don't think any of the Rice vamps ate or drank.
IIRC, the "classic" vampires - Dracula, Varney, Camilla - I don't think they were ever seen to eat or drink.
And, the legends vary depending on the region. For example, in Chinese folklore one type of vampire drinks spinal fluid, not blood.