I made some enquiries.
It turns out that the dispatch release, computer and ATC flight plans were all prepared by Nordic in Sweden and sent to Spanair dispatch office in BCN to hand them over to the crew. That's a fact, and so it wasn't the pilots but Nordic's operations dispatchers who made the mistake.
The flight did not match the crew's roster and that should have raised a flag, but since both destinations are in Spain, both are served by Spanair and flight time from BCN is similar, the pilots may not have noticed. ATC simply gave the clearance to the filed destination and the flight followed its flight plan.
It would be unthinkable for anyone at Spanair, or anywhere else in Spain to mistake SVQ for SCQ or viceversa.