Have a great time in Barcelona. If you plan to visit the Picasso museum or the Sagrada Familia, get there early! The lines can get pretty crazy by lunchtime.
Do check out La Rambla and make sure to detour through La Boqueria — I’m still regretting that I didn’t get a chance to step into that foodie paradise when I was there. Also, there was a great churros & chocolate place (‘ Granja La Pallaresa’) nearby, down one of the side streets. The churros you find in the States pale in comparison.