What are the advantages of the moon for staging solar system missions?

It seems to me a suitable orbit for planetary mission staging would be on the ecliptic plane, but relatively near earth. There's no point in having to deal with two gravity wells, one is bad enough. I know there are many other factors to consider; the radiation belts, long-term atmospheric drag, space junk, but most of the energetic costs are already paid in our atmosphere or slightly above it. Sure, once you get to a suitable earth orbit, the additional energy required to go to the moon is negligible, but so are the energy savings you get by launching from there; everything leaving that moon station has to be lifted from earth anyway, and anything leaving from there will have to climb out of the moon's well. Besides, the complexity and vulnerability of the logistics increases exponentially with isolation from earth. Surely, "operational experience" (such as assembling, servicing or mating large vehicles) gained in hard vacuum and zero-g can be acquired easily nearby, no need to go all the way to the moon to get it. It would be a lot easier staging deep space missions in an area that can be quickly and easily reached, and where they can easily and quickly be deployed. And if something goes wrong, any infrastructure required to mobilize a rescue, repair or corrective measures would already be in place.

I can see an advantage to an orbiting moon base if we were initiating a major program of lunar exploration, one that would require maintaining and supplying multiple extensive facilities and scattered personnel on the lunar surface.
But that doesn't seem very likely unless we find a huge reservoir of easily exploitable resources there.

But you can assemble and launch a Mars mission from earth orbit a lot easier than you can from lunar orbit. And you save yourself the effort, risk and expense of developing, implementing, and supporting a capability that is essentially static and inflexible. Local orbiting stations can be used for many other purposes, which helps pay for their upkeep. An orbiting moon station is an expensive, single-purpose advance base on the edge of nowhere. Am I missing something?

In my opinion, the human space effort was severely damaged by our need to get a manned lunar mission ahead of our cold war rivals. It was all about national prestige, not space exploration, and we paid too much, not to mention the Soviet effort that wound up being mostly wasted. The spectacle was magnificent, but there was no payoff, and it did not lead to any useful follow-up. Saturn boosters were not used on missions after Apollo. Yeah, I know, old obsolete tech is inefficient and expensive, but it also is dependable and we have accumulated experience operating it. And once you scrap it it often proves very difficult to replace. We got the bugs out of those old systems and we can depend on them. And we have old timers with the experience to quickly modify and adapt them to unforeseen uses. We're still launching spacecraft with Atlas rockets.

To a lesser extent, the succeeding programs, the shuttle and space station, had similar issues. Our most successful and cost-effective space ventures have been in scientific/exploration payloads, communication and earth resources missions and navigational satellites. And our manned missions have benefited greatly from primitive, but cheap and reliable Soviet era boosters and manned spacecraft. We should not be repeating our old mistakes, and any new systems we do develop should be designed with long-term viability and easy modification and adaptability in mind, not just short term optimization for today's glamour mission.

The Spitfire could defeat the Luftwaffe's best fighters, but most of the bombers were downed by Hurricanes.