I think it's likely difficult to know the exact impact foreigners are having on prices. It makes up such a small percentage of total houses sold I'd have to believe it's minimal at best.

Plus, to qualify for the investment visa you had to spend at least €500K...which would already put it out of the income bracket for the majority of Spanish residents. Of course with that said it's not unheard of for condos and other properties to inflate listing prices specifically for outsiders who don't know any better.

So if there is an impact, I'd have to think it would be limited to tourist-driven communities like Ibiza. But, again, I'm only speculating.