Parts of this new path are a paved street

are you sure the track goes like this? my trace and the aerial image show another route

There are several really good hiking trails on Sifnos. See here: http://www.sifnostrails.com/map/
I started naming the tracks (numbers 1, 3, 5, 10) I recorded with my GPS with the "official" numbers. I'm not sure, if I did it right, so please feel free to improve and extend OSM on Sifnos with respect to hiking