This may have been already suggested or implemented. In order to view trends of certain collected statistics it may be worthwhile to use metadata to link similar or related surveys taken over time. This would allow users the ability to not only see past trends but also build projection models. For example, airport delays may have a seasonal peak and additionally linked to periodic weather fluctuations.
From what I see this site provides a solid collection of various descriptive statistics and there is great potential for building more complex inferential models.