Personally, I would say a metro pass would be of more use. Its much easier to navigate your way round on the extensive metro system. Can't remember what a 'several day' pass is, but to give you an idea you can get a 10 trip ticket for �7.40. Tickets are available at the machines at all metro stations. If you want to 'sightsee' the Barcelona Turistic Hop On Hop Off bus runs 3 routes (but I think it goes down to 2 in Sept) and this costs �20/day or �26 for 2 days.