I have a very high regard for Simpson, having played many of his courses on the European continent. In my humble opinion he was as good as Colt, and maybe even a bit more creative (and mad perhaps as well...).
When I restore Colt courses I go for the soft touch, focus on bunker and green complex restoration, look for good tee positions that add length if required without significantly changing the strategy of the hole.
In the case of Cruden Bay I think the course is unique because of the unorthodox way Simpson and Fowler used the terrain to create some very unusual holes. Its not so much the bunkering or greens that catches your attention (although some of the greens such as green 3 and 6 are very clever), its the unusual and smart little things (such as the fact that its very difficult to keep your ball on the green on the 16th green, esspecially with a tail wind when you effectively only have a landing area of a few m2, but when you miss the green at the back you have an exciting chip/put back. Is this UNFAIR?).
What would I change? The only hole on the course I really do not like is the 9th, which in my opinion is so bland that you almost would think Simpson put it in the round to make you realise how exciting the other holes are. Holes 10, 12 and 18 are good but not great and all the other holes are very very good!
To change the 9th is very difficult, and probably would require significant shaping/earthmoving. Maybe move the tee back to the right again towards where the current path leads up from the 8th green and make the hole a short right dogleg par 5 playing into the prevailing wind, with a lower and higher split level fairway...... I'll give it some thought, and maybe I should offer the club to my views....