I have never been to this site although as it happens I will be making a visit at the end of next month.

So without having seen the circle my initial reaction would be to re-errect the stones. After all, the builders (for whatever reason) decided to build a stone circle. I can't imagine they would mind it being put back up as a tribute to their skills / beliefs etc?

In my opinion any fallen stones / tobs etc which have fallen over time should be re-errected as long as it is done in an appropritate way.
i.e. you can be sure how the stones originally stood / safe to do so etc.