Did my first Scotland trip last summer. Old Course, Kingsbarns (2x), Castle, Crail, Elie, North Berwick, Gullane, Muirfield (2x).
If I was doing it over again I'd play Kingsbarns only once, and skip the Castle Course. I wouldn't miss Crail and Elie for anything, especially Elie. Elie might have been my favorite of the whole trip.