Whoah...... there are some great points being raised here by NG. When do you draw the line under a sites period of active use in terms of serving the human spiritual condition? I know I get a profound feeling of being that much closer to that abstract notion of 'Mother Nature' or whatever - not to mention feeling more of a part of 'humanity' - whenever I plonk myself down within a 'circle or haul my frame up to a summit, so it's still relevant for me - whether I'm deluding myself or not. So I guess NG's right and it never really ends. Speaking from experience I've seen a lot of what you could term 'religious' activity at many a site.
Some circle sites remain full on places to be even when there's hardly anything - or nothing - remaining to be seen. Perhaps the founding act was truly enough? And at the other end of the scale would anyone credibly argue that sites such as, say Grey Whethers, Strichen, or even Knowth are any less 'real' for being reconstructed so you can actually experience them more or less as they would have been. Other, untouched sites may be quieter, more atmospheric, but are they better? Dunno. Guess it's gonna take a lot of thinking to work this one out.
Interesting that there may be less of a tradition of summit burial in Scotland? Only been to about 20 tops, so can't really comment. Guess I need more fieldwork. England, too.