I Don't Think People Can Be Reduced That Much to Political Stereotypes
I don't watch Downton Abbey so I am really out of my depth here, but I imagine conservatives watch it for almost the same reasons liberals watch it: It's an interesting situation and the characters seem real.
Sorry to disagree with you, but I'm so bothered by the liberal power structure (academy-journalism-entertainment-government) Otherizing conservatives that I'm really resistant to Otherizing ourselves.
I don't think the attraction is "pining for a bygone age." Ridley Scott (someone also rumored to have Tory sympathies, by the way) was very fond of making movies set in an an alien environment. And not just in Alien. But in Someone to Watch Over Me (set in the alien environment of the fantastically-wealthy urban rich), White Squall (alien environment of yachting), Black Rain (alien environment of Japan's tatame culture), and so on.
I would wager money that shows like Downton Abbey appeal to science fiction and fantasy fans. Similar appeal, but different trappings. Just as in science-fiction and fantasy, the technological level (or TL, for Traveler fans) is different from our own and imposes some of its own force upon the setting, and the culture is fundamentally different from our own. There is that same appeal to the viewer as in First Contact stories in trying to figure out The Rules of a different culture.
I'd similarly wager there's a big overlap between consumers of sci-fi or fantasy novels and historical fiction. The latter is, though it's seldom noted as such, essentially branch of speculative fiction itself.*
I guess I'm just bothered by this "bygone era" business as it seems to assume conservatives pine for an aristocracy and aristocratic privilege.... I cannot think of anything that is more directly opposite the truth of the situation.
* Game of Thrones
is an popular example of overlap between the genres, being, as it is, a mash-up of real European wars and personalities (the War of the Roses being the most obvious shout-out) and some dragons and Red God sorcery. The books are much concerned with a style of medieval warfare that I personally never heard of before the fictions of GoT.