Years of overtourism have greatly damaged the unique nature of the city center. This does not mean there aren't interesting corners of weak signals. You can embrace the presence of massive flows of tourists as a formidable opportunity to get a snapshot of humanity. For instance, I recommend walking down the La Rambla the epicenter of overtourism - for light observations clothing, haircuts, appearals and curious travel apparatus from all over the world.
New concepts exist not only on a contiuum but as part of an accretive world where old and new co-exists. At the Mercat dels Encants you will get a different angle on the everyday objects. This flea markets exposes all types of clothes, cooking gears, and antics in their second or third lives.
There are many corner stores in the city, mainly owned by Chinese immigrants. These places are commonly referred to as el chino offers a full catalog of goods imported from China that people living and visiting Barcelona need to solve problems in their everyday life. For instance, with a visit of Bazar Oriental, you'll see that many great innovations trend towards the counter of corner convenience stores.
Finally, La Central is a bookstore + café where I hang out to observer local interacting and overhear discussions about their projects and concerns.