Off topic, but related: Can a radar center offer flight following to a
plane not equipped with a transponder? I would guess no, but I'm curious.
I think that you can have an IFR clearance and at points along the
route not be in radar coverage. In those cases you get a much larger
zone of protected airspace around you, and you have to radio in your
position at compulsory reporting points.
As for flight following, I would think the value would be pretty much
useless. The whole point is to gain a second pair of eyes for you on
the ground with the assumption that you are still responsible for
separation from other aircraft. If the folks on the ground can't see
you on their scopes, then there's really no point to flight following.