Duncan,
As I recall, the 18th was a layered fairway in MacKenzies's day. I am not quite sure what that entailed, probably just a set of terraces up the latter half of the fairway. I wonder if there's some way of lessening the slope by starting earlier, or if that is simply too expensive. I like the idea of people leaving buggies at the bottom of the 6th hole to take you back up the 18th. I also like the idea of some sort of ski lift. Most of us don't need the facility - or didn't in my case - but some innovative method of getting visitors and unfit golfers up the slope in reasonable shape would make the experience far more rewarding, even though these are not the bread and butter of the club, whose members won't even notice the 18th. I don't like the idea of later playing the top holes just to make up the round - the 5th is rather a makeweight hole, although the rest are terrific.
I'll give you another thought, to which I have no answer. The 16th is a fun par 4 but the long walk back to the 17th tee is poor. The 16th was post MacKenzie. Can you somehow re-route the course after the 16th to bring the 17th back over the stream to a green some way in front of the present 18th tee allowing you a long par 3 finisher up the hill (or bogey 4 within reach of most amateurs). I think it is the drive across flat land to the bottom of the hill, from which we can not get up, that is the most depressing part of the present hole. I know you get too many par 3s but you get an extra par 5 of some substance.