
According to the Standish group research on average 45% of a software features are never used and only 20% of features are used always or often. It means that on average you could develop two times simpler product and sell it for the same price. Potentially gains can be even bigger, for the enterprise scale systems two times simpler product often means four times shorter schedules and ten times simpler integration and testing.
There is no other way to discover what features would be actually used, than to ask the real or at least potential customers, preferably after letting them to try some features live. One of the tools for aiding the feature categorization is the Kano model of customer satisfaction.