You might be ok. It tends to be the coastal resorts that get swamped in August - people flee the cities because they’re too hot. So whilst there will always be tourists, many of the locals/local tourists will be on a beach somewhere else.
We stayed a block out of El Ravel, which is a section of the the old city but a little less nice than the gothic quarter, felt much more of mix of local residents and stores to serve them, but still a mixture of touristy establishments.
It was walking distance to La Rambla, some museums, the Gothic quarter. Also walking distance to the subway.
The Casa Eliot Hotel was a converted apartment building, clean comfortable and nice decor, but nothing special.
I think you’re the first person in this thread who didn’t stay somewhere in Eixample 
From what I’ve read so far, I’m thinking El Ravel might be a little more gritty than what we’re looking for.
It’s really quite spectacular from the inside, it’s worth it to fight the crowds and go in.