I know people who use the Caledonian Sleeper multiple times per year.
Last time I travelled on it I sat at a table in the club car with a freelance journalist who made a return trip every week. He was on first name terms with all the stewards which considerably speeded up our drinks service!
On my last trip to Glasgow, I had the odd experience of watching a current affairs programme on my tablet computer, knowing that the presenter was on the train! (We had met him in the Club lounge, having just arrived at Euston after recording it earlier that evening)
(I didn't watch much of it - iplayer reception wasn't brilliant on a moving train).
I presume that the 373 nol sets must have had adjustable steps (like the pendolinos).
They did. But not for that reason. 373s did not call at any normal platforms in the UK - only the International platforms at Waterloo and Ashford, which were built to the same designs as those at Brussels Midi and Paris GdN.
But I recall at Lille they extended steps down to reach the Continetal-style low level platforms.
How they would have worked on the North of London services I dont know.