Alex,
I wasn't able to play it - which if you do, they have a 2 week notice period where you must set a tee time prior to driving there (learned the hard way) - but was accompanied around the property on a personal tour. Mullen is in the middle of NOWHERE! One hour from the nearest lodging and food, other than that the course offers. It is a spectacular site that was laid out so that the golfer would see nothing while golfing; a complete getaway from the world. The 'clubhouse' and access is set on a hillside that hides the course. A meandering path, which I would assume is not easily walked (I was carted around everywhere on the tour and so could not properly address if the course is exactly walkable or not) leads you through small hillocks until you reach the outhouse (I forget the name for it, Uncle Ben's Cabin or something along those lines) which is in the location of your typical clubhouse - where the nines return.
The most fun I have ever had on a golf course was at Ballyneal. I could play that course over and over and never get tired of playing it. The quirky features and use of fescues are perfectly complimentary to create a 'natural' course. The dunes are different than that of Sand Hills as they are more 'choppy' with what would be the equivalent of whitecaps to the Ocean or Great Lakes, not rolling dunes. The fact that there are no markers whatsoever is representative of the way golf should be played. I was unable to really grasp the type of membership at Sand Hills, but understand it is national: half of the membership concerned with the prestige factor and their handicap at the "no. 1 course in America built since 1980", and the other half true golfers who love the sport; Ballyneal's membership was reflective of what I would assume was the initial design intent: fun, dedication to the true sport.
So, my suggestion is Ballyneal