I actually haven't seen a lot of plus fours, but it may signal that the place is about golf, rather than any extraneous activities. I'll never forget finishing our second 18 at Bandon Dunes one day, trudging toward the clubhouse, when we saw an older gentleman (70+) wearing plus fours sprinting to the first tee to start his 3rd round of the day (we had seen him throughout the day). It was one of the more uplifting things I've ever seen.