I don't know if I've ever touched on it before or not, but it seems from your comment, I haven't because I know you're one to go out straight to study something and inform yourself.
But anyway...
Summer football tournaments have always been somthing quite a bit special and different in Spain. Every country has them so it's nothing new. But in Spain they used to be seen as something important and there were specifically two that were the greatest of them all (infact those two are still the most important by miles even when they've lost the mystique they once had) and they aren't organised by the clubs most would expect.
The most important one was and continues to be the one organised by Cádiz CF and the Troféo Ramón de Carranza
The next most important one is the tournament orgnaised by Deportivo La Coruña and the Troféo Terésa Herrera
These days summer football tournaments in Spain have at most cult followings and their history is just the folklore told by those that remember the hugeness that they once represented as a football festival that would conjure up a week of carnival spirit similar to a World Cup with the greatest players on earth visiting your twon and being seen in the streets.
Today these types of things like the Emirates Cup which we have in London are referred as pre-season tournaments and of very little significance if any at all. But back in the day these things were no pre-season friendly events used to generate renevue for the club. They were AFTER the pre-season and the first big test that clubs, coaches and players would take seriously.
Being invited to one of the two premium tournaments in the shape of the Ramón de Carranza or the Teresa Herrera was an honour for a club anywhere in the world and would be used as a showpiece.
These days the very few that continue to exist in Spain are played as one off games and not 8 or 10 clubs involved so as to keep the tradition of the annual event alive. The Joan Gamper organised by FC Barcelona was one of the biggies but nowhere near the prestige of the aforementioned tournaments organised by Cádiz CF and Deportivo La Coruña respectively.
I remember reading this book (above) on the history and downfall of the mythical summer football tournaments that would move travelling fanbases from the other side of the world for a whole week. It basically tells the story of the fall of real football to be honest which is quite sad.