Much of the “draw” in Spain are things and places that survive from hundreds of years ago. That and warm-water beaches.
Neither are really expandable.
Barcelona has just a few tourist “draws” (I know Barcelona very well) - the Barri Gotic/ciutat vella (Gothic quarter), the old medieval city - which includes the Picasso museum. La rambla, the old main drag, which is lined with tourist businesses, the mercat (public market), the port, mainly the yacht harbor, the beach, the various Gaudi sites. And thats it.
Barcelona is a huge city and the tourists crowd into @5% of it.
There are some other bits that, imho, should rank, as destinations, with anywhere in Europe, but arent really huge tourist draws. The fortress of Montjuich, the Museu Nacional d’Art de Catalunya, which is very grand, even the Miro museum, if you like that sort of thing.
https://en.wikipedia.org/wiki/Museu_Nacional_d%27Art_de_Catalunya
I’ve never been to Spain, closest was southern France. I spent 5 weeks in ‘72 and another 5 weeks in ‘76. Traveled all over, and a bit into northern Italy, in the Alps. A beautiful trip is along the Chateau de Loire and especially Chenonceau castle. and Chambord. The gardens at Chenonceau are just beautiful.