The spiral path at the top is the spoil that Colonel Drax and his men threw over the side.
The EH geofiz find was part of the construction sequence not any kind of ceremonial pathway to the top.
If there was a built spiral pathway is would still be there and there would be no point in creating new paths (as previous visiters have done)
Silbury would have been white for a year tops.
This was shown at the experimental longbarrow built in 1961 on Fyfield down.
Marlborough Mount did once have a spiral path but this was a later addition.
It was a Motte & Bailey in 1290.
Hatfield barrow never had anykind of path, being greensand it would quickly deteriorate.
Silbury now has a new rabbit proof fence small enough for any visiter to leap over.

The Hecateus quote is usualy attributed to Stonehenge.
Glastonbury doesn't have a spiral or maze around it.
Air photos show this quite clearly.
PeteG