@DavidJohnson
worth discussion indeed.
Two points I'd like to throw in:
1) Many more Spanish people live now abroad than a few years ago (ever heard Spanish speakers outside London 5 years ago? Walk through the likes of Birmingham, Liverpool, Manchester now...) due to the poor employment prospects in their home country. So it's not only BCN tourists / business visitors using these flights.
2) Above point will not justify this serious amount of additional capacity - agreed. So thinking about it earlier, I felt most comfortably with taking the view that this is a massive muscle exercise by IB&Co as owners of Vueling to defend their home turf against FR and EZY, the likes of 4U/LH from Germany, etc.