These guys are doing fine at Saratoga Golf and Polo, from what I understand:
https://www.saratogagolfpoloclub.orgThey have the full club amenities: golf, tennis, swimming. Golf is 9 holes. Course dates to 1890's I am told. They recently did restoration work on the course I am also told.
There are some cracking stand alone 9-hole Clubs and courses around but I would say success in selling it to members depends on a few factors that are not really strictly golf related. Member/player expectations being one of them.
In the right location where playability in decent ground conditions is available close to 52 weeks p/a and with overall low level staffing, sensible course maintenance practices relative to the terrain and a small pavilion Clubhouse with limited food/beverage then I could see a stand alone 9-hole Club/course being a success. Success here not defined as a pure money-making venture but rather as more of a break-even style of long-term existence operation. What the nearby competition is like would also be a key factor.
Our modest 9-hole club fits this description other than it's only open about 30 weeks a year. Staffing is generally 1 in the house rotating among half a dozen part timers, 1 greenskeeper full-time and a 2 or 3 part timers there, and a pro/house manager (often the 1 in the house).
Members volunteer for larger projects: new roof on clubhouse, new paint, tree removal, new signage, excavating, grading, etc.
Menu is limited (burgers, wings, sandwiches) and small buffets. 5 beers on tap. All the liquors: vodka, gin, bourbon, rye, rum and ancient bottle of Galliano. Few people set out to join a 9-hole club. But, a good club atmosphere and a fun course, regular competition, and a spirit of camaraderie make any course a good place to spend one's recreation dollars and hours. It's not always easy to see that from the outside, though.