Good grief, you just started a thread on the last 7 years of my life. I used to buy golf courses for one of the large golf management firms, and we extensively used demographics to evaluate the relative strength of a market. The best place to invest is a formula based on population, drive times, average household income and number of golf courses, and some other factors, but you're right about new courses having an impact. It's also the hardest to research or predict.
One thing I can tell you: if you built a golf course on the island of Manhattan, the ratio of golf courses to people would be very good. That said, there is technically a golf course in Manhattan (governor's island) that nobody ever plays, so maybe I'm wrong.