I have a confession we were at one point going to marry at callanish as it was special to us but then some other people did who were apparently the first to do it for 1000 years so it kind of pissed on our fire and the specialness of the idea wasn't really the same plus it would have been difficult to get my granny and her bad legs over to lewis and other guests.
Now though I'm quite glad we didn't get married there, but it still remains special to us.
I don't see a big problem with people getting married at stones as I doubt it would happen that often already in orkney they have the bus tours taking people round sites so people wise i can't see that increasing hugely and causing more damage plus the weather can be crap there so i doubt if many folk would find it ideal.
I do think though to get married at a replica is a bit odd doubt if it would feel quite the same as the real thing or have the same vibe.

There are however alot of replica pictish stones around more often than not to show in a solid way what the stones were originally like (if damage has occured or they have been moved to bigger museums for preservation) I 'm not sure if they have erected any of the 'fakes' in original sites though but I don't find that too bad an idea with repect to preserving the location of the ancient site I suppose with an ornate marker.
any way thats my tuppence worth!
love
carolinex