I had started a thread about 3 or 4 years ago asking essentially the same question, Ben.
I belong to a private club that has a golf course that is well over 100 years old, and has been meddled with by numerous well intentioned but uneducated Green Chairmen over the years. Generally speaking, I don't think most classic courses need an architect to tell them to remove trees, restore putting surfaces, and change the mowing patterns of a fairway.
However, my mind was changed significantly about two years ago when our club started working formally with Jeff Mingay toward a Master Plan.
There was a plan developed for our 6th hole, based on a few board member's desire, to remove the blind 2nd shot on the long par-4 which they thought was unfair. It was "passed" and the plan was to move forward but our Superintendent had Jeff out to review first. The board had budgeted somewhere around $70thd for the plan, but it took Jeff about a day to tell the decision makers that 1) it would cost dramatically more than $70thd, 2) no matter how much earth you move it would still be a blind shot, and 3) it wouldn't fit with the classic architecture of our golf course.
So, Jeff really helped the club dodge a bullet there.
Recently, we are in the later stages of a master plan at the golf course. I like to think I know the course well, but the different ideas he has come up with in the process is mind boggling. Not drastic changes, just tweaks really that on the whole would create a dramatically better golf course (in my opinion).