I agree that naval bases are purchased less often than air bases, but I probably buy one about every third game. When playing Japan, and you have just taken India and have your fleet sitting in SZ 39, you can ruin the allied player’s day by building a naval base in Kwangsi or Hainan and getting back to Japan 1 round earlier. Sometimes when playing the allies, I’ll buy one in Norway after capturing it. When you need one, you need one and they are worth every penny.