Hi Robert,
I want to respond to your statement, "it seems to me that if advanced civilizations were common, then one might choose to make its presence known." Upon reading it, I realized that I did not expound the point I was making sufficiently.
A civilization with foreknowledge machines simply would not make contact with a civilization without them, because this would invite conflict. They would be able to look ahead to see when a given civilization would attain viewer foreknowledge themselves, and when contact would be initiated with that civilization, so they would not have to wonder about when to make contact or debate the matter amongst themselves.
Think about it this way, such a civilization would not stay hidden out of fear, they would stay hidden out of compassion. If a civilization without access to viewer foreknowledge (i.e., a future-blind civilization) were to encounter any other civilization, the future-blind civilization might form an aggressive posture due to fear of the unknown. This might cause the future-blind civilization to attack, in which case the future-sighted civilization would have to defend itself, and this would obviously not go well at all for the future-blind civilization. So, it may be that graduating from the future-blind stage is a universally understood prerequisite to first contact for civilizations everywhere.
So, from this perspective, on the assumption that all civilizations advanced enough to achieve interstellar travel would also be future-sighted, it would not be the case that, "if advanced civilizations were common, then one might choose to make its presence known." Just thought I'd add these ideas to my previous comments.
Warm regards,
Aaron