You might make more in the buffet car from the 100 cheap ticket holders than from the 10 who have paid through the nose.
If you only cater to the 10 you might not need a buffet
Obviously the levels you pitch fares at aren't simplistic. A return on BA with a saturday night stay is far cheaper than one without, because they know business travellers who want to get home for the weekend are willing to pay more than leisure travellers for the same seat. On the other hand they also know that there aren't enough business travellers to fill every seat on every flight. The trick is to sell the cheap tickets while not cannibalising the expensive ones.
But that would mean two people travelling together paying the same price that one person on their own was paying. I can't see that being workable.
50% on the second ticket (or whatever the current discount is)
If you pay £30 for a railcard and immediately pay £34 less for a rail ticket it hasn't really cost anything, has it?
Nor is it a £34 discount. And the hassle of getting a railcard. And the extra risk when you find the railcard has been signed in the wrong type of pen or some other nonsense.
If you want to get more non-railway leisure passengers onto the railway (not something the railway really wants to do given how many routes are at capacity), getting rid of railcards would clearly be an improvement, especially F+F and Two-Together. Whether the extra revenue would offset existing railcard revenues (and the bad press in the express about 'discrimination' against old people if senior railcards weren't also free) is something for modellers.
In the meantime I'll be driving to London in August for a family holiday, because the hassle of driving to the station, parking there for £58, organising a railcard and paying £176 for the journey (including the railcard), compared with putting £35 petrol in the car, siting in private listening to an audio book and driving to London, and paying £75 to park in London.
(The extra wear and tear of an extra 300 miles on an already owned and maintained car is negligable)
Would a railcard discount with no hastle of filling in a form, and no money to pay, make the difference? Probably not, but it certainly doesn't help.