so is there any actual evidence that foreign home ownership is causing meaningful housing price inflation in Spain? or is this just uninformed pandering like it is in the US
Meaningful is a weasel word here. Even 0.1% price increase which would be impossible to measure directly still adds up across the entire housing sector. But, equally important is simply the number of natives prevented from buying the home they want because someone is getting a vacation property.
If builders would have built N units knowing they could easily sell some % them to foreign buyers but now they can’t, then you might lose the whole supply. And all the knock on effects for contractors, suppliers, etc