Filled in: let's hope it produces some results.
I keep spreadsheets for all of my long trips, so possibly could complete the final question on daily spending reasonably accurately. However, the overnight component is coloured by the use of aires etc and Britstops, so I have placed estimates: I guess that it's only a data aggregating activity rather than a search for precise answers.
As others have said: it depends on what is there AND although I may be prepared to pay "more than £5, up to £10" but I would prefer to pay £6! Ultimately, I don't have to accept their offer but increasing potential stopping places must be advantageous.