Couple of other ‘developments’ that might improve the Avebury WHS.
1) Tarmacking the main NT car park which, at 5 quid a bash, is definitely warranted (though there may be legitimate objections from the archeo community to doing that). Tarmacking would certainly allow better wheelchair access from there to the High Street though.
Alternatively, 2) allowing disabled parking at either the Avebury & District Clubhouse car park, or the small NT car park in front of the Hengeshop.
Tarmacking the NT car park would certainly be an improvement that's for sure.
The Avebury & District Clubhouse LS, that's the cricket pitch area isn't it. I would have thought a nice small unobtrusive teashop on the perimeter of it adjoining the path from the NT car park to the henge would be a nice place to have one. You then get a chance to have a cuppa just after arrival or on the way back before returning home. It could be designed similar to a cricket pavillion and supported by 'spot' foundations so that the archaeology disturbance was kept to a minimum. In fact it could almost be the cricket pavillion if it was rebuilt in a new position and doubled as a tearoom.