In the TNG episode "Sarek," there's at least one other Vulcan-Human hybrid in Sarek's entourage named "Mendrosian," I believe. Or something like that. And in the STAR TREK cartoon, Future Spock tells his Childhood Self that he's a cousin who's got a bit of Human blood. Young Spock, in the cartoon, simply accepts this, without question, which suggests that there must be a lot of this going on, certainly by Sarek's time. Outside of the ears, though, I don't really see the appeal a Vulcan offers a Human ... what, with their anal retentiveness and embarrassment at every outward show of emotion. For a Human, surely, it must be like walking on broken glass ...