To improve participation, some financial incentives could help. For example: 1) Cash prizes for the top 3 stairwalkers as registered on the website. 2) 10 pence off your Tube fare if you took the staircase exit in/out of the Tube station.
A possible way to extend on your concept (or maybe you already had this in mind).
If the app timestamped your every update, your wellness history can be graphed against time to provide some feedback. A bit like a stockmarket chart, which tells you whether your "family" parameter has been going slowly downhill for the last 2 years, or if your "work" parameter goes downhill on particular months.
You can use that feedback to warn yourself of an likely downward trend or make you reflect on why certain months are good/bad for you.