Still too much gravitas for dapper. There's a certain devil-may-care foppishness invoked in bitching about fashion as an alternative to gallows humor. Put another way, he needs to be stylish without being a default authority figure, which is more of what I consider Colin Salmon's wheelhouse.FWIW Ive only seen Salmon in Arrow, which was a character that never got more carefree than a sad, burdened half-smile. So I may just be underestimating his range.
He usually plays characters with a commanding presence. But that's kind of how I picture Steed. Your take on him seems more foppish than mine. I took him as concerned about his appearance, but no more than your typical British gentleman. And his use of Casual capital Letters struck me as more "assumed British superiority" than "foppish dandy".
I was more of a TNG than a DS9.
Siddig el Fadil aka Dr. Bashir from Deep Space Nine would be good as Nic. He was recently in Game of Thones, too. He’s still very handsome and charming.