The Moon is a detour on the way to Mars, not a stepping-stone.
Precisely.
Maybe not. There is water ice on the moon to support a base. And the lunar regolith is stiff with He3. If we can discover how to get He3 fusion working then possession of the Moon isn't just the key to Mars, its the key to the Solar system.
If we never get He3 fusion working ... yeah, the Moon is just a big dumb rock. Unless the Chinese build a base there and get all "the moon is a harsh mistress" on us!
(though in that case the very easiest way for them to achieve space superiority would be to launch an Orion into earth orbit)