La Rambla, Sagrada Familia and Park Guell are inundated, step a few blocks away and it's generally much quieter, plenty of small plazas etc.

Last time I went, I visited those places, but I stayed in a tiny hotel in the gothic quarter and walked from there to Park Guell instead of using the tube, stopping to get ice cream or coffee, letting my four year old play on the park and so on. Step away, slow down and enjoy it.