This is so cool. I wasn't aware of that quote, so thanks.
I'm still developing what I'm putting in the book (also called SWS, published by Thames & Hudson late this year or early next) but thoughts developed about it which were too late for the film.

It struck me that henges were generally in use for a long time and soil from the ditches always made up the banks. Plenty of people agree that the banks were seating for spectators but have always had this fancy idea about how 'special' multiple ditch henges must have been. I think it's more simple. If a site becomes more popular over time and populations are increasing too, you need bigger banks to create more seating.

I reckoned that if you could prove that at a multiple ditch henge, the bank was made from the soil of both ditches, it would add a lot of weight to the theory.

Guess what the latest soil analysis at Thornborough showed...

Bingo!