The Carrowmore visitor centre and this http://www.themodernantiquarian.com/site/8884/listoghil_tomb_51.html are the same, still open when the staff have left. The Carrowmore complex is vast and 'securing' it would be next to impossible. I prefer to show up when they've all gone anyway, having he place to myself rather than sharing it with half-interested tourists. Newgrange and Knowth would be places I'd visit more often were they less 'secure'. Modern 'security' measures often ruin these sites.
CCTV at Skara Brae? Brings to mind the American officer in Vietnam: 'It became necessary to destroy the town to save it'*
*http://en.wikipedia.org/wiki/Ben_Tre