It might be a problem to keep your best developers working in Barcelona on Spanish level salaries if they are good, young and fluent in English. It's not just the absolute salary numbers: the relative purchasing power of even decent Spanish salaries is pitiful.
I only stay here because I'm not so young anymore and have a family, but otherwise I would move somewhere that might be twice as expensive but pay more like 3x.
On the other hand, Barcelona is a great place for young people to live.
I know plenty of people here in Barcelona who could earn much more in their home countries, but choose to live in Barcelona for the better quality of life.
A web developer would probably earn twice as much in London (where I'm from) than here in Barcelona, but they would have to spend all the increase on rent to rent a nice apartment. Forget buying in London on a junior- to mid-level salary, but here you could buy a nice apartment in a nice part of the city.
Not to mention the weather, scenery, beach, cheaper restaurants and bars (with better opening hours), lack of violence, and sheer excitement of being in a foreign country.
