Hello,
I travel to Spain at least once a year just to decompress. I use BCN as my entry as it is easy for me. Last year I traveled from Barcelona to Santiago de Compostela by train and bus. Took about 10 days and could have easily used a few more. If you are thinking about staying north I would heartily recommend Haro for a drop or two and Bar Otono in Pamplona for bites that are made in heaven. I found Zaragosa interesting but ultimately one of those places that you would have to be from to want to go back.
I didn't care for the Guggenheim (I'm not a fan of modern art...if you are going to draw a picture of a horsie then please make it look like a horsie. Don't paint a series of vertical lines and then make me read an explanation telling me it is a horsie.) And I found the Dali Museum quite disturbing (he was heavily into genital mutilation).
Sitges is always good to see how the other half lives.
I will be in BCN again in October and plan to visit Cadeques (sp?) then drive west to take in Galicia and then down through Portugal and Andulucia.
In BCN I would recommend Irati for easy and cheap bites (don't throw away to toothpicks) and Hostal Rita for a good sitdown lunch that is muy barrato. I also enjoy Bodega de las Palmas for a late night tipple.
happy trails

