Was it Josh Pollard that when saked about restoring Avebury said, "To what period? The mesolithic?"
Many monuments are multi-phase. Which phase do you restore to?
If a standing stone fell a long time ago, who is to say that its 'destruction' wasn't a phase in its cycle. Under the same argument though you could say that re-erecting it is just another phase! As would the restoration of Avebury or whereever.
I suppose any work on a monument should not be seen or pushed as restoration (unless the period is precisely displayed and made clear), but as today's contribution to the monument. Certainly, Stonehenge could be rebuilt with newly cut stone and it would still mean the same to the majority of the hoards that visit it if it's still in the guide books! It's no longer a monument and has become a moneyment!