Nimoy is so subtle, maybe I'm seeing things that aren't there, but when Plasus introduces his daughter as a "work of art" and Spock responds that he's never met a work of art before, I think he was interested. Also, Droxy may have seem shallow, but apparently she was schooled in various art forms, like painting. It's hard to make blanket statements, but it seemed like Vulcans' had a high appreciation of art forms, so a beautiful artist may very well appeal to a Vulcan's tastes.
Also Spock is thinking this line: If the lovely Droxine knew of the young miner's misery, I wonder how the knowledge would affect her. He's thinking she's lovely.
Another quote.
SPOCK: Extreme feminine beauty is always disturbing, madam.
That's what I'm basing my previous comment on.
Maybe Spock would have like to keep her in his home on Vulcan, filing it with artwork so it's nice when he comes home on leave.