I went last summer in the beginging of June and it wasn't any worse than where I live in VA, imo. mid to high 80's I'd say.
I personally was not impressed w/ Barcelona. I loved the Sagrada Familia, absolutely beautiful. Don't listen to the guidebooks that tell you not to go inside, since it's amazing to look up once you get inside to see how vast it is. Also, if you pay to enter you can take the elevator to one of the steeples and walk the stairs down. Took us about an hour to get in the elevator and it was supposed to be $5 or so, but no one collected our money, so it was free lol. It was a lot of fun to see all of the different points of the basilica since you can see different angles as you walk around.
Gaudí's park, Park Güell, was also a lot of fun to wander around, but wear comfortable shoes when you go. It's a bit of a walk from where the bus drops you off and the park is huge! Other than the park, I'd skip his apartment and the Casa Milà, the building he created. It's fun on the roof, and the outside looks impressive, but the Casa Milà was highly under-impressive on the inside, so I wouldn't waste the 15 dollars. Everything else I went to in Barcelona wasn't overly impressive. We went to up Montjuïc to where there is a fort of some sort, but other than the view of the ocean, it wasn't worth the trip.
We stayed in a hostel right off of Las Ramblas, lots of bars, tourist shops and restaurants, plus the subway is right there on the strip. Never had any issues, although it was rather loud at night when we were trying to sleep. I can't really recommend restaurants since I went w/ my sister who is a vegetarian, so we never ate tapas or anything like this, since they all have meat in them. We mainly stuck w/ random places we could find that appealed to her lol. HTH