The level of detail (granularity) in data MAKES ALL THE DIFFERENCE in whether data is valuable or not. The number of variables and the level of detail of the data is critical. Simple data results in simple applications that have limited value. The world is complex and applications can help us understand the complexity. So government departments dumping any old data just so they can say they have contributed to open data without making sure it has some value is a waste of time.
Also, there are thousands of apps out there but only a few are really popular because they meet a need. Building something that meets user needs is the first most important thing to consider when building an app, webpage, software, etc.