I just finished 5 days with my family in Barcelona. I personally approached Barcelona with great apprehension based on all the stories in this forum and others. Plus, both my sister and niece had their purses stolen (on separate trips) in the last couple of years in Barcelona.
But we had no problems. Here are some of the things I did to ensure a safe trip, and one with peace of mind:
1. Use a money belt, or (men) stick your wallet in your front pants pocket (this worked for me).
2. Get a back-pack or purse that both zips and locks, like those sold by Pac-Safe. I got a back pack and my wife bought a nice 'evening bag'. In addition to the many security features of these bags, the bag straps can be clipped onto 'immovable' things like chairs and tables, so they don't wander off at the restaurant table.
3. Read and familiarize yourself with all the pick-pocket scams. Then, just be aware of what's going on around you. My wife and I were deep in the Raval one day when a young man started following us. Nothing too obvious to the casual tourist, but my antenna was up. I turned around at glared at him several times, as if to say "I've got your number". He finally smiled at me and moved on. I watched him stroll to the next female tourist, where he scanned her purse, decided it was too much of a challenge, and then he moved on again.