I suspect the laws did not carefully consider when spectators can profitably contribute. Instead of waiting until 2018, you as director can take advantage of a loophole in the laws and request your spectators to "speak as to fact or law". My requests are below.
Is a player at the next table a spectator? A spectator is defined as "any person in the playing area other than a player or a tournament official" (unless the director specifies differently). So it depends on how "player" is defined. The laws don't explicitly define "player". There are numerous uses of "player" that can only apply to the players actually at the table, such as "no player shall take any action until the Director has explained all matters in regard to rectification." (L9B2)
Therefore, the players who are not at the table are almost certainly "spectators" for the purposes of that table and bound to the laws for spectators. This matches the understanding that if there is an infraction at one table, players at the next table may not call the director ("Any player, including dummy, may summon the Director after attention has been drawn to an irregularity.")
As I interpret the laws, this means that players at another table cannot point out scoring errors. Obviously, it is common practice to point out scoring errors and this is a good thing to have happen.
There is another tangential issue. Most people interpret the laws as saying that a director must rectify any irregularity he becomes aware of. However, in practice, most directors do not do this if they are kibitzing a table or happen to hear a table because the table is near to where they are sitting. IMO, this law is better interpreted as giving the director the right to intervene whenever he notices an irregularity but not the responsibility.
Anyway, if you take the view that you as director don't have to intervene, then when should you intervene? The answer, I think, is that you certainly should have all of the rights as a kibitzer. When you see my requests for kibitzers, you will see that the director is extremely likely to intervene for any of these irregularities.
Law 76C1: "A spectator may speak as to fact or law within the playing area only when requested to do so by the Director." I suspect that the authors of this law were visualizing the director making a verbal request while at the table, not publishing a general request to rec.games.bridge. But I think this law allows the general request.
I request (and prefer to obligate) spectors to speak in the
following situations, and only these situations.
PRIOR TO THE START OF BIDDING
Anything to help get the right players to the right table at the right
time playing the right cards and having their cards in their hand
facing in the correct direction.
This assistance includes players do not knowing what they are not
supposed to know prior to play. So a spectator should point out that
North is about to open the wrong traveller.
FOLLOWING THE COMPLETION OF PLAY
Anything to ensure that the recorded score is the same as the actual
Any suspected errors or misleading impressions in the statement of the
laws (including whether or not to call a director) given by the
director or opponents. Additionally, any suspected errors in omission
made by the director.