I believe the EH Commission has directed that an intellectually robust definition of "setting" should be developed. Hoisted petard time maybe?
In any case, ANY discussion of setting is likely to be on our side I'd have thought. Can the creation of an ideal setting be said to include the insertion of a multi-million pound visitors centre within the viewshed of the monument?... Not to mention the fact that it's a bit passé ... !
As for the cost issue, we might have a head start there as well. Everyone knows the sector is skint, and getting worse. However iconic Stonehenge is can such a disproportionate lump of the cake be bestowed on an interpretation centre for that when most other places are lucky to get an information board???