“Spain as a holiday destination is still so popular”
I don’t think it is. Spain was only ever popular because it was cheap and convenient but nowadays it certainly isn’t that cheap and is no more convenient than any where else. The average british tourist just wants nice weather and a beach and doesn’t have much interest in foreign languages or cultures, so the charms of Spain are lost on them.
Living in the province of Malaga, I notice that it gets only slightly busier in July/August, but even then the roads are still quiet and the beaches / restaurants / apartment blocks are only half full at best.
It never seems to get busy any more and as a resident I like it like this.