Unjust speculation 1: “the ruins of any dismantled monument are likely to lie somewhere between the two megalith quarries”. Not really, there are lots of other motivations for where you build a circle, why assume the positions of the two quarries were the likely determining factor? What about views, water, unknown commemoration etc etc like other monuments?

Unjust speculation 2: there was a proto Stonehenge in Wales for 500 years. But isn't it equally likely there was a proto-Stonehenge (if there was one at all) somewhere else, including, equally probably, near Stonehenge?

Isn't there a stronger argument for spending their funding looking in Wilts rather than Wales? What a hoot if it was found on the route of the road leading to the tunnel!