Hmm, I think a huge thing you've overlooked is using the moon as a staging area like maximum Derek said above. We stockpile fuel, food, etc. And maybe even begin to manufacture vessels there to save from using a vessel stressed from an earthly launch. Would make Mars trips easier, asteroid missions, the like

Edit to add: I wouldn't be surprised if there's still some forms of metallurgy or other processes that can be discovered with a continuous scientific base on the moon, that they couldn't attempt on the ISS or replicate here in vacuum