Many years ago, when I was living in Madrid (Barrio de Salamanca), Puente Vallecas and Villa Vallecas were out in the 'burbs' where people went on weekends. Cercanias didn't go there yet and public transportation to Vallecas was pretty sparse. But Madrid has grown outward. Now the Cercanias and any number of Bus lines serve Vallecas; and I guess like Torrejon de Ardoz and Alcala de Henares, it is now considered a fashionable place to live.
As for the historical perspective and the spelling of Vallecas with a 'k,' it sounds like an Euskera preference to me.
Things change!
I've even got a cuñado living in Leganés. Go figure!

[This message has been edited by Eddie (edited 01-16-2001).]