This looks like the makings of some interesting arguments.
On the point of prescription charges.
Of course in Spain one pay according to their income.
In Andalucía the computers in the farmacias automatically link with those of the Tax Office and thus what one must pay is easily seen
What will happen to say a person from UK ? How will they prove what their income is and who will decide what they should pay on a Spanish prescription?
I just don't see how it stands a chance of working in practice, unless the DWP provide all the required info when they issue the EHIC, which of course will vary according one's income for any particular year.