First a quick note about Li Bai and Du Fu. They were friends and prominent poets during the mid-Tang Dynasty (712-770). Li Bai was perhaps the more prominent of the two. He was equally known for his love of nature and his love of solitude.
In "Drinking Alone Beneath The Moon," the moon is primarily a symbol of beauty—and its distance.
You want to speak about it as a symbol of abundance, harmony and good luck, but this poem is a bit doubtful about the moon's capabilities.
It shines on Li Bai and provides him with a shadow to dance with. Is that a happy image. It's up to you to decide about that. There are a lot of different translations, but it's said that Li Bai died by drowning when he tried to hug the moon's reflection. This poem foreshadows that event.
Its ending speaks about death. Here’s one translation of the poem’s last lines—a not so happy ending:
I make an oath to journey forever free of feelings,
making an appointment with them to meet in the Milky Way afar.
Drunk at last, we drift apart in space —
Lost to worldly things, until some day
We'll meet again, beyond the Milky Way.
Is the moon’s distance happy or sad to you? If you see the solitude as happy, you may be able to make a case for the moon being a symbol of abundance.
As for Du Fu’s poems about the moon. There are a lot of them. One that I like is, “Moonlit Night.” You ask about how the association with abundance and harmony informs the poem. I’d say there the symbol is more happily traditional. The moon, again associated with distant beauty, lights up the world for the traveller, and seems to calm him.