Yes, I do open houses for my condo listings and have had some success before.
Success story #1: I had an open house where a neighbour and his friend who was visiting stopped by out of curiousity (or maybe for cookies, lol). The friend had been looking for houses for months, but after looking at the condo unit, he decided that he didn't quite need a big house.The Buyer checked out the parking, came back to view the unit with his Realtor with an offer and the unit was sold!
Success Story #2: I had booked viewings with a couple and when we went to visit the 5 units, one partner kept comparing them to a condo unit she saw at an open house earlier that day because she was walking her dog in the area. We went back to see the unit the next day and my clients bought the unit!
It's true that it's mostly curious neighbours that stop by an open house, and the odds are slim of a buyer walking through but you just never know! At the very least, I get feedback on the price and condition of the unit and get to meet some interesting people!