Patrick,
What you had the same architect(s) doing the same style holes? Pinehurst isn't quite as homogeneous. You could still always have the original 18, and could access/play it any time you liked. But then had alternate routings as well. Wouldn't work in a big, high play club, but in at a place like Sand Hills, with relatively limited play of a very golf-savvy group, finding alternate paths through the course, such as it was, would be fun.
Is Ridgewood a case of taking three wonderful nines but from them crafting an even better 18? If you remove any memory of history there, and take away any concept of tradition, and just have the 27 holes lying there, is a composite 18 such as they used for the recent PGA Tour event the best 18 available? Going back to the beginning of your discussion thread, is there any less "ease of routing" in the composite 18 than there is among the original nines?
Going back to Sand Hills and "ease of routing", from strictly the routing point of view and ignoring what we both agree is the greatness of the current 18, couldn't you perhaps integrate a new set of 18 holes such that an intermingling produces two wonderfully routed courses? If C&C's assignment was to do a 36 hole complex all at one time, do you think the original 18 would have emerged intact? Again, just thought experiments, but interesting to ponder.