Out of interest, what is the argument for reducing resolution other than space concerns? Fitness data is not really space-intensive. I recently ran a marathon and the associated GPX file is less than a megabyte; the FIT file is about 180KB. I don't really think even 30 years of regular running data would come to much. I appreciate cycling data will take more space but not that much more.

My point is, it seems like once you have put in place the habits and technological solutions necessary to store fitness data, it actually takes more effort to reduce the resolution of older data. I'd rather have data and not want it than want it and not have it, but then I am an almost pathological hoarder so maybe it's just me.