There are a number of reasons to conduct open housed with developing a customer base being one of them. Depending on the time of year and location the success of an open house can vary greatly but on the whole they a great marketing tool and should not be overlooked.
I know it's difficult to get buyers to come to an open house but if it's advertised everywhere. Ex. post on the MLS, KSL, craigslist, trulia, postcards to neighboring homes, postcards to target areas such as to renters, or move up buyers etc. depending on the type of home etc. Door knock the area beforehand. I've known many agents who have had success doing just that.
Also, when you have the open house put up literally dozens of signs. In a class that I'd taken on 'selling in a buyers market' this top agent from CA said 40 signs! Put them literally on every corner, I've sometimes had 2 on a corner to catch people's attention. People just get used to seeing signs on corners that they don't pay much attention to them unless there are a lot of them!
I hope that this info. helps!
Becky Nay, GRI
Keller Williams Realty