Take a cab. Myself and two friends were mugged walking those three blocks on our way back to El Caminito after our lovely lunch. We took a cab there, but thought, "well, it's just three blocks, what could happen?" The answer - my friends were physically assaulted, pushed up against brick wall by a pair of 15 year olds, threatened, hit, purses stollen, and were very rattled. I saw it coming and ran, the guys didn't catch me, por suerte, but I saw the attack on my friends, and I felt horrible that I couldn't help them.
Bottom line - better safe than sorry.
PPS. My husband is from a different part of La Boca, and he told me not to walk to or from El Obrero. I wish we had listened.