I have been a real estate agent for almost 12 years. I know a lot of agents do open houses and some houses sell through an open house.
The question in my mind is not open house or not but how your agent will drive traffic into the house. Nothing is more frustrating and unproductive than having an open house with nobody or only a handful of people through.
On the rare occassion that I do an open house I have teamed up with other vendors (mortgage company, title company, insurance, etc.) to provide food and beverages, ice cream scoops, bottled water, etc depending on the listing price range of the home, sometimes we even have done a theme, like Oscar night, superbowl party, etc. We sent out either handwritten invitations or torpedoed the area with flyer invitations, started advertising in the local publications 2 weeks before the open house. We'd always always have at least 20 directional signs to drive additional traffic in.
I am not a big fan of just throwing out signs and/or having a one-line blurb in the real estate section about an open house, sitting in the house and praying that someone will show up. It has to stand out. The key is to get as many people in as possible and even if it doesn't work for those people, they may know someone else who may not yet be actively looking or be out of town. Some of my open houses have sold that way.
Other than that, open houses are usually for newer agents to build their business. Most agents don't hold the open house to sell the house they are holding open but to find new clients. That's what they are thaught when they start real estate.
I think open houses can result in a buyer, they just have to be part of an overall marketing strategy. In a market like this you want to get as much exposure as possible but I wouldn't hold my breath on getting the house sold through an open house.
If you have any errands to run for a few hours and your agent has a well-thoughtout plan how to drive traffic to your house, why not. It won't hurt and after all it will be your agent's time while you do what you have to do. People do walk into open houses that they would have never looked at otherwise and end up buying it.
HTH