I have visited Dornoch but once and played the course twice, so my opinions should be weighed accordingly. My votes:
1) Redo
2) Leave
3) Redo
1) Clubhouse -- I would certainly defer to the opinions of the locals, however, there was nothing about it that I regard as memorable except for the display of the Carnegie Shield. The Shield itself deserves a more worthy presentation, though the result needn't be Trumpian. Despite the disruption that a full, start-from-scratch rebuild would cause, I suspect that a new design could serve players and staff much better than the current one, and it would offer the club the opportunity to build something truly distinctive. Extending the William Morris quotation to the structure itself ("Have nothing in your house that you do not know to be useful or believe to be beautiful.") I don't think it would be sacrilege to replace or massively renovate the current house. Build something eminently useful or inarguably beautiful, or both. One of the loveliest, most magical courses in the world deserves it.
2) 7th and 8th Holes -- I studied the course for years before I got to play it, thanks primarily to this site and your book, which I gladly purchased months before my visit. The 8th was the hole I anticipated more than any other, and I was not disappointed. I like the 8th just as it is, and to the argument that it is echoed in the 17th, well, I would say that the very resonance between the two is part of the charm of the course. The fact that the 17th introduces an option that the 8th lacks (the short-drive-dowhill-approach) enhances the appeal of the 8th as is. Moreover, the difference between the two holes in terms of background visuals and overall routing -- towards the Firth vs. uphill and inland -- makes them distinctly different. To me, the experience was like being given a mulligan, or perhaps enjoying a slice of blueberry pie and then, awhile later, a piece of pecan pie. Readers of a certain age may recall the Lovin' Spoonful song Did You Ever Have to Make Up Your Mind? about the conundrum of choosing between two sisters. Well, in the 8th and the 17th at Royal Dornoch, lucky are we who get to enjoy the differing charms of both.
Furthermore, though I understand the frequent criticism of the 7th hole, to this player of modest ability the 7th was a welcome relief after the intimidating 6th. The green contours are lovely, and they are severe enough that I doubt birdies come easily even to better players. In any event, a birdie there must be earned. Perhaps bunkering could be added or modified to increase the quirk or the challenge, but as a 9-10 handicapper I'm happy with the 7th as it is.
3) 11th & 12th -- To be honest, the 11th green/12th tee is the least memorable patch of land in the entire course. I took many photographs in my brief visit, and even so, that particular area is like a black hole in my memory. My instinctive response is: If locals are considering change there, by all means make it. Having just taken a look at my few photos of the 11th green and 12th tee, I would certainly vote to make some changes. A few tweaks could spice things up...