Adding to what George and Tom noted, get a lot of before, during, and after photos from the air and the ground. Also annually. by season, for at least the first 10 years, shots of special holes to see how the course has matured. These photos can be digitized and stored efficiently and safely.
In addition to the architect's thoughts, also document the developer's/founding members' explicit objectives/dreams for the course. Information on the construction process, including the major contractors, special circumstances or difficulties encountered, as well as a time line of major milestones would be interesting.
As a financial guy, I would like actual costs vs. budget, for the total project and by major component (e.g. land, design, clearing, drainage, construction, irrigation, clubhouse, etc.). However, the owners of some non-equity clubs may not want this information for public consuption.
Continuous records should also be kept of significant events such as capital improvements, important tournaments, club awards, special visitors, and very unusual weather conditions (and their impact on the course).