First, let's establish some principles to guide us. Number one is that developments should be judged by whether they mainly benefit the WHS or the applicant.
There isn't another.
Judged like that, a lot of recent and pending developments should be opposed. Including anything by NT. They're over-dominant. It ain't their WHS. They have 2 museums, a shop, a cafe and now they want to add another retail outlet to take a further share of the tourist pound from the other outlets in the village (who have to pay them rent).
The principal motivation for the new outlet is to make money for NT (and it won't make much judging by how they run tea rooms elsewhere), not to enhance Avebury so it's a definite no-no.
90% of what's need in Avebury is a 15 mph speed limit and speed bumps. Anyone who opposes that doesn't truly have the public interest at heart.