You should be able to do a factory reset, see How to factory reset emonPi - #2 by glyn.hudson. That is a couple of steps short of “flattening” your pi, but I agree a “reset data only” function would be useful, many users experiment and then want to start with fresh empty feeds, a factory reset also looses all their settings and processing that they have been experimenting with and finally got the way they wanted, it would be useful to keep that.