Donal:
My intent was not to try and approach a "World Top 500" or anything close to it, just to find a less controversial way to repackage The Confidential Guide if I ever wanted to do it, by focusing only on the courses I would recommend seeing. [It would be a lot easier to deal with Greg Norman or Jack Nicklaus on that basis, as I could include some of their work and say nothing about other bits.]
The problem with a "World Top 500" is just who would it be for? There are a lot of unimaginative types who would think that list should include all 300 Jack Nicklaus courses [or alternatively, all 400 Donald Ross courses], because they have a narrow view of what's good in architecture and all of those courses fit their description. Whereas my own list would focus on where you might find a great hole or cool feature you've never seen before ... for example, it would certainly include Painswick, even though I am sure that most people would not put that course in their top 1,000.
I have not counted up the entire list nor tried to figure out the percentages of courses in any given area that make the list. 40% is a high figure, but of course my sampling of courses is far from random ... for years I traveled on exactly this basis, going to check out any course which someone who sounded knowledgable would recommend.
Here was my list for Scotland (sorry no time to put it in order):
Highlands: Brora, Royal Dornoch, Boat of Garten, Pitlochry, Nairn, Cruden Bay, Royal Aberdeen, Murcar
Midlands: St. Andrews (Old and Eden), Kingsbarns, Crail, Elie, Lundin Links, Blairgowrie, Gleneagles (Kings and Queens), Carnoustie, Panmure, Kingarrock
East Lothian: Musselburgh Old Links, Luffness New, Gullane 1-2-3, Muirfield, The Renaissance Club, North Berwick (West), The Glen
West Coast: Western Gailes, Royal Troon, Prestwick, Turnberry (Ailsa), Loch Lomond, Shiskine, Machrihanish, Askernish
I realize that the cut-off point for this list is quite arbitrary and hard to distinguish. Why Panmure and not Montrose? Why did I leave out Lossiemouth [maybe just an error, there]? Why not Kilspindie, which I've recommended here in the past? All are fair questions; but on that basis, I suppose I could recommend nearly every course I've seen on some level or another.
I guess my bottom line is that if someone was traveling from America to Scotland, I would tell them they weren't wasting their time with any of the above, instead of thinking they have "seen it all" just from playing the Open rota, and could move on to other destinations instead of ever going back. Indeed, any of the sub-groups listed above would make for an excellent and varied golf trip, without all of the ridiculous racing around on narrow roads that most Americans do in order to see all the "greats" as fast as they can.