Is Myranda Royce snobbish about the Sistermen in TWOW because they’re poor, or because they’re not integrated into the Vale political polity, or some other reason?

Good question! 

I think there are a couple different factors going on:

The Sistermen are not part of the mainland but rather out on the extreme periphery of the Vale:

  • Because the Sisters became part of the Vale after the Battle of Seven Stars, they don’t have the cachet of having fought for the Andals and the True Religion (in the same way that a certain kind of WASP looks down on people who didn’t come over on the Mayflower or whose ancestors didn’t fight in the American Revolution) and are instead provincials.
  • Because they live far off, they’re not a regular part of court life, and although definitely the highborn families would be treated as highborn, they certainly wouldn’t have the cachet of the inhabitants of the Vale proper.
  • Because they don’t live on the mainland, they don’t share mainlander concerns about mountain clans raiding or growing seasons or mountain passes being closed off by snow, etc. 

The Sistermen are moreover a historically rebellious and quasi-criminal part of the periphery. 

  • Before the Andals came, the Sistermen were pirates and slavers, neither activity likely to make them popular with the people they steal from or the people they steal. And to the present day, a big part of their economy is smuggling, and wrecking – the mainlanders despise honest merchants, so these guys are going to be seen as the lowest of the low.
  • As the mainlanders see it, the Sistermen started the Worthless War by being greedy pirates who poked the wolf one too many times, and not a small part of the mainland suffered as a consequence.
  • Then after the Arryns rescued the Sistermen, they rebelled against them during Aegon’s Conquest, and then against them and the Targaryens during the Blackfyre Rebellions. 

And finally, there’s the whole inbreeding/webbed fingers and toes thing, which probably means they’ve interbred with the Squishers…

Is the Royces’ status as a principal house of the Vale at odds with their seeming pride in their First Men heritage? In a country noted for the value placed on noble Andal blood, whose First Men were mostly dispossessed and driven to become barbarians in the mountains, you’d expect any remaining First Men noble houses to try to assimilate into the Andal order – but things like ancient runic bronze armor seem to suggest the maintenance of a strong, persistent and distinctive First Men identity.

Actually, no, I don’t think it does.

I see the Royces as something of the Vale’s Loyal Opposition. They’re one of the most powerful Houses in the Vale other than the Arryns, they’re older than the Arryns (and Valemen are super-snobby so this counts), and no one challenges the Arryns except for them. Hence why a Royce cadet branch ended up at the Gates of the Moon, why we see Royces as Lords Regent of the Vale, why Royces marry into House Arryn (and I would imagine vice versa), why it was the Royce of Runestone who besieged Jonos Arryn when he turned traitor, and why Bronze Yohn was one of the first to turn against Littlefinger.

I see them as somewhat assimilating and somewhat accomodating. On the one hand, the Royces have converted to the Seven and are definitely bang on side with the whole idea of knighthood and tourneys and the like. So they’ve done the big ticket things that matter. On the other hand, they’re very proud of their First Men heritage – the runic bronze armor, the marriages into House Stark, etc. – but I think in a way that works for the Vale. Being arch-traditionalists, the Vale are very into heritage, and the Royces being Seven-worshipping knights means that the First Men stuff is made “safe.”