It's resulted in graphs that look like this: https://www.statista.com/statistics/576081/number-of-sexual-...
The Andalusians and Valencian/Catalans are both located in the Mediterranean and they can have huge cultural related differences and traits, and they can differ a universe from the Castilles and the Northern Spain which is a bit less "partier" than the always-sunny Southern part of Spain. Also, you have microclimates and microcultures in these regions. Yet, I repeat, a common background it's stated by pure practicalism. It's either that, or isolation and poverty.
Because if you have a look on the map of Spain, you'll find that half of the map of Iberia it's crossed by mountain ranges creating isolated regions up to very recent years (relatively compared to the Middle Ages), making the cultures of Spain anything but homogenous.
Right now, the main problem Spain seems to have is the right wingers wanting to take back over and run the country into the ground (again) in pursuit of the kind of things you’re espousing. And the only thing really stopping them is the Catalans, who would rather not have anything to do anything with the rest of the country because of how obnoxiously intolerant it is.
Hint: the Spanish Francoism, Catalan's burgueoise nationalism and the Basque-Navarre ones came from the same nest.
If any, every nationalism in Spain (no matter which side, either independentist or statist) was bound to the old regime and later... money and crushing labour movements.
Inb4 the Basque Left and ETA... ETA joined the labour movements in Francoism as a quick alliance against Franco. After that, the nationalist side took far more precedence that the universalist pro-labour one. Far more.