I don't think you'd be totally on your tod Tuesday.
I never gt as far as Rousay, but I remember Unstan as being quite sympathetically restored with the whole concrete and skylight thing. So I think I know what you mean, it's mebbe not what you'd ideally want, but in the face of a dodgy mock-up of corbelling, or open to the elements, there is some merit to the way they do that kind of thing up there.
To be honest, I generally feel that when they go for it, Historic Scotland seem to do a better job than their counterparts south of the border :(