I'm totally black-pilled on this subject. Spaniards are hardly having kids anymore. IIRC the birth rate is somewhere around 1,1 per woman. The original/indigenous population will gradually be reduced both by lack of reproduction and by being forced out due to the house price to income ratio. I'm not sure the local authorities can do anything meaningful. Most alternatives will be in breach of EU legislation.
I am pleased to have experienced Ibiza before this really kicks in, and slightly guilty of being a tourist and thereby contributing to the fall.
There are solutions, but I'm afraid an international shock like 1848 is the most realistic alternative to get a different kind of politicians elected. Although don't expect these to be kind and generous centrists. It could go many ways.