I live south of Barcelona and have visited the City many times and have accumulated several maps of the City. I had never noticed really, but you are correct! My Valencia map is the "correct" way round – i.e. North at the top. Other towns along the coast however are as Barcelona - Gandia, Denia, and Calpe for instance. Javea is the same orientation as Valencia. The really odd one is Teulada-Moraira which shows the Mediterranean on the left! This means South is shown at the top of the map.

I suspect town and City maps do not abide by the same rules as world maps. When you are out and about with a city map it is easier to hold in landscape rather than portrait mode so if a City is longer North to South than East to West it will be depicted left to right rather than top to bottom. Perhaps Teulada-Moraira maps got printed upside down!