highrail, did you happen to check whether it was standard or narrow gauge?
As for the Martha's Vineyard Railroad, it is not 100% gone. Some of the embankment just north of Edgartown can be found if you look closely. The raised area in the middle of this picture is the embankment off Norton Orchard Road.
A significant portion of the Edgartown Golf Course perimeter road run along the former ROW, and the embankment can be found in the woods to its northwest.
Looking at aerial imagery:
That's the one bit of remaining ROW that I wasn't able to get permission to visit - the homeowner wasn't home.