You have an almost entirely leisure market at the weekends, unlike the weekdays which are dominated by the two rush hour flows. First class in particular sees very few business travellers or full fare tickets being used, for obvious reasons (weekend first). Most first class tickets (not upgrades from standard) are advance purchase, as are a great many in standard class. A very different market.
Another thing to bear in mind - a quick run through the posh end doing weekend upgrades can easily raise two or three hundred quid on a busy train. That's minimum effort, cash in the bank - give em a seat that's already there, feed em tea and biscuits that are already on board, etc. There will be one hostie behind the buffet, punters bring their tickets up and ask for their complimentaries. If you do a proper catering job, you need a chef and an assisting host, on top of the first host doing the buffet. Even if you still do the cheap upgrades, those two extra staff members have already wiped out your profit, and some. You are now running at an overall loss, and solely reliant on selling meals to recoup it. Having the space to seat your diners means less space for your upgraders, so possibly turning some away. You may have a queue of diners down the the train, but where will you put them all? Or do you scrap the cheap upgrades altogether and hope and prey you can churn out enough meals to make the same money? But then who will pay full price for first class; remember that your business travellers aren't there today?! You'll need the full weekday offering, that's another host to take the trolley through, and another dent in the takings. And so on. It really is a better bet simply to do cheap upgrades and fill the seats!
