I was just reading I Am Legend by Richard Matheson (it’s very good, so far) and noticed a reference to “Stoker and Summers.” Stoker I recognized, of course, but I’d never heard the other name. Apparently he was something of an authority, although a difficult-to-read-one, on vampire legends, as this link explains.
I can’t say for sure that the name was the inspiration for Buffy’s last name, but it seems like a logical train of thought – you’re writing a vampire story, you do research. Is this verified in any of the countless “insider info” type books about the “Buffy” series? Any other details fans would like to share?