Yes: worth three or four days, for Gaudí buildings found nowhere else

Barceloneta beach is a fifteen-minute walk from the old city

It suits least those who hate summer crowds or booking ahead

La Rambla is the most pickpocketed street; wear bags at the front

Least worth it in August, and in the wet September and October

Barcelona has Gaudí and the sea; Madrid has the stronger museums

Most worth it from late May to mid-June; the full answer inside