Yeah, I would say add Madrid (it is very different from Barcelona and worth it in its own right even if not as tourist oriented) and then go either north or south but it would be a lot of hassle to combine the two.
I would say Andalusia would be a good option and do a night in Cordoba, then a couple days in Seville and a couple in Granada. You can take the VY flight back to BCN directly from Granada.