Thanks for the comments, all! The brainstorming and questions are definitely helpful - I often find myself interrogating the basic premise of a setting/character/plot to help develop it further, and hearing feedback in this manner helps in a similar way. 
The question of feeding is especially interesting to me because I’m especially concerned with the concept of modern vampires as a “superior” version of humans and their hierarchical tendencies both within and outside their own ranks. I kicked around the idea of the “feeding on werewolf make you strong like ox!!!” possibly being placebo - that the superiority that one individual might wield over another based on their diet, lifestyle choices, etc amounts to little more than a fantasy grounded in certain ideas of what makes a “real” vampire. And one who doesn’t hunt humans might be doing it for practical purposes (it’s less conspicuous) and be branded a coward and weakling, while maneaters might be viewed as thuggish but viable threats, and those who willingly and regularly go toe-to-toe with other supernatural creatures as some scary motherfuckers, whether or not there’s a physiologically significant benefit to drinking different kinds of blood. But even if there were, I guess it’s because I’m drawn to the Fantastic Racism side of things, tying in again to the theme of “forbidden” relations - how would a member of such a group reconcile their internalized belief of superiority with feelings of More Than Apathy towards a supposedly “inferior” creature? Particularly an “apex predator” vampire with a human? (Especially if a human still manages to get the best of them somehow! There might be interesting possibilities there.)
And yeah, animals aren’t “vegetarian”, but putting it in scarequotes is useful shorthand for the idea people are trying to get across. 
In Twilight’s case, the “vegetarian” label was probably meant to carry connotations of weakling, bleeding hearts, etc, even though many vampires who abstained from human blood did it more as an ego/personal morality thing than out of sympathy and goodwill to humans, whom they considered below them.
Speaking of, I shouldn’t be too surprised how immediately this swerved into a Twilight discussion, so I might as well throw in my two cents. I think its popular Totally Not a Fanfic successor 50 Shades is seeing a similar reception these days, which is the reaction from readers outside its core demographics or target audience (“people with good taste” one might say, haha) to a perceived decline in literature… as well as the integrity of a completely fictional species. The truth of the matter is that stories like Twilight and 50 Shades have always existed, albeit not so visibly; the former’s popularity, however, left a significant impact on the fantasy/YA market that endures to this day. For better or worse, elements of Twilight have been absorbed into the larger “vampire mythos” that make up the modern supernatural genre as we know it, though much of Twilight was borrowed by previous contemporary works. It’s an inevitability of folklore that certain concepts will change over time to reflect modern sensibilities.
I even have a good example of that in this very thread. Take the comment from @Apillis for instance: “just saying ‘sparkling vampires’ makes them sound more like flowery fae than the literal devil-spawn that they are meant to be.” Funny that fairies themselves were once believed to be demonic in certain cultures, often malicious, “troll”-like in appearance with a penchant for kidnapping. The hobgoblin experienced the opposite evolution - it went from a friendly household spirit to Tolkein’s huge, deadly uber-goblins. As people have already pointed out in this thread, vampires have undergone many such transformations over the years, from a metaphor utterly FRAUGHT with sexual overtones to… well, maybe they haven’t changed much, in that regard.
I’m admittedly mystified that some people seem to zeroing in on sparkling vampires as much as they are, but I’ll chime in anyway. There’s nothing inherently degrading about having qualities that react to environmental lighting - we don’t view the glint of, say, a dragon’s scales, or a knight’s armor, or the point of the sword as a detractor from their potential to intimidate.
Which brings me to another point. @Galador I’d love to hear an explanation on what’s particularly “gay” about “sparkling” in and of itself. It’s gay in the same sense that colors, festivals, decoration, etc can be gay (bright, loud, cheery) but there’s nothing that inherently ties it to someone’s sexuality. And if there were legitimately gay vampire characters… so what? A character can be straight and effeminate (and sparkly!) without it detracting from them as a character. A character can be gay and menacing. A character can be x and y, because if we constrain ourselves to a certain mold of what is “acceptable” to a straight, white, cisgender male audience within a given age bracket, then we’re closing ourselves off to an incredible range of possibilities of who we can use to tell a story. Like I said in the OP, I’ve been concerning myself much more with the character side of things, and how it plays off their “condition” (species, race, affliction, whatever you’d like to call it). Being badass doesn’t have to be synonymous with a certain idea of masculine.
Not calling you a homophobe whatsoever, by the way, but I would love to see a homophobic vampire character cursed with perma-glitter, which would be hilarious if done well (and not played straight as a “LOL GAYS” joke).
I’m also uncomfortable with the underlying implication from some posts that anything that appeals to a young female audience is inherently inferior. In the larger scheme of things, these stories are mostly in the minority when you compare those that are targeted specifically to a male demographic (though they may amass a large female audience regardless). That being said, I’m aiming for something a little more generalized and darker than YA - while I did actually enjoy Twilight despite a lot of its problematic points, there was groundwork it laid that it was unwilling to explore, likely due to Meyer’s general puritanism.
TL;DR Though I’m really interested in logistics discussion too, unfortunate implications of some remarks. I’ll probably chime in later with more detail of what I had in mind after my errands, but thanks again for all the thoughts!
