Philosophical question - what is CS for? Why do we subsidise it? Is its purpose to be a rich person's plaything ("the Deerstalker") or is it providing an essential public service?
Like many bits of railway it exists simply because it was too politically damaging to get rid of it. The SNP wanted to use Westminster cancelling it as a political attack point, but Osborne called their bluff by throwing £50m (??) in for new trains and leaving them to fund the rest, and now the Scottish government is stuck funding it.
If you were cynical you might suggest that making it an expensive hotel on wheels is a long term wheeze to enable future cancellation by publicising how much each rich person's holiday was being subsidised. I wonder if the Highlands now have so many tourists that the marginal lost business of ending the sleepers isn't even relevant (how many people wouldn't go without the sleeper, rather than just travelling a different way?)
Yield price it and let it stumble on until the stock needs replacing. I can't see any way of making it more profitable, rather the opposite as rail inflation is probably higher than they can inflate the prices.