Paul: I followed your post and wanted to respond. I took your question to imply "What aspects of a course challenge all skill sets ?"
My peers and I on the business side of the golf business believe the following to be the message for success: "Look hard and play fair". Here in the Northeast we have a highly rated public venue named Ballyowen, an inland "links course" ( it was constructed mostly on an old quarry, this no trees). Their recipe to sucess is just what I stated above, plus providing a good level of service before, during and after the round. The holes most challenging on the course are the par 3 holes, which involve carry over water; a difficult shot for the average golfer. The better player, from the rear tees can shape their shots and score well but still feel challenged.
Two other courses asociated with Ballyowen are Black Bear and Wild Turkey, both of which offer interesting holes. The signature hole on both courses is a par 3 over water; Wild Turkey's is over an old quarry and Black Bear's is across a sculpted curving pond. Neither course is designed for PGA Tour play, but both are successful (ie making money) and are being enjoyed by a broad spectrum of golfer's of varying abilities. The "average golfer", a 20 handicaper, feels good at the end of the round because his/her score was ok and he/she enjoyed the day.
Another course fitting this bill is Pine Barrens, in Jackson, NJ. It allows the better player to challenge the course by taking agressive lines of play (#4 Par 4 - fade off tee and long iron in - aggressive play or drive/lay up and chip on for a par putt for the shorter hitter) or the average player the chance to chip and putt for par. The corridors are wide to allow for finding an errant shot and the greens have some slight movement but a generally flay (with the exception of the par 3 12th). The last five holes are a good test for players of all ability - #14 par 3 over water(signature hole) #15 good 2 or 3 shot par 5, #16 sculpted do leg par 4, #17 long par 4 intot he prevailing wind and #18 good 3 shot par 5.
Testing the abilities of golfers at all levels on the same course was successfully done by many of the old masters. They allowed for multiple lines and angles of play on each hole to allow players of different skill and power the same opportunity to be successful. Par is par on the scorecard, whether it takes 2 to get on and 2 putts or three to get on (the third being a chip shot close) and 1 putt for par.
A successful way to challenge all players on current courses is the design of the chipping/collection areas on green surrounds and approaches. By reintroducing the ground game here in the US (where most of us have learned to fly the ball onto the green, you add the element of uncertainy to the ball path (inconsistant bounces). The average player can get the ball up onto the green as can the skilled player. If the ball were being played from a sand bunker, the better player will get out and ontot he green while the avereage player willtake two strokes to get out of the trap about half the time.