During Din's delivery sequence, multiple scenes feature billboards marketing a given luxury with rich people while the people in the world mimic those scenes (a billboard with two women locked in arms contrasts a woman helping an elderly woman walk, a rich man sitting alone with his drink contrasting a group of men playing a board game on the street). This highlights the movie's theme of how the luxuries and riches that everyone strives for can never compare to making warm bonds with the people around you.
At first glance, it seems like a small detail that the wish dragon rules say "Can't go back in time" in place of "Can't bring people back from the dead". But then it dawns on one: it's meant to subtly foreshadow to the audience that not only is Long capable of bringing people back from the dead, but it will come into play.
While rehearsing his reunion with her, Din has a difficult time coming up with something to say to Li-Na after all this time without coming off as phony or creepy. It's only once Din's suit falls apart that he's able to form a genuine speech for Li-Na about how he misses her and still cherishes their childhood bond. This is meant to frame how Din and Li-Na will have a genuinely good time together once he sheds his "Dan" persona.
Long's teapot is made entirely of jade, a representation of his greedy nature and how he valued wealth above all things; even stating that he owned a jade palace. Near the end, his teapot is made of simple white porcelain with golden trimming. His character growth thanks to being with Din and his loved ones have cleansed his soul of his greedy vice.
The first Fridge Logic below implicitly carries with it a justification: Long wasn't thinking of a plan that would result in Pockets' failure and Din being safe, he was acting on pure selfless instinct for the first time in his life. In his past life, he surely would have hesitated to do anything except maybe flee; by contrast, Din needed to be saved now, and if that meant the reformed Long Taking the Bullet, so be it.
Fridge Horror
After sharing his backstory, Long soberly remarks how in hindsight, he did his previous nine masters a disservice by giving them material wealth instead of what they actually needed. Kind of makes one wonder how many lives Long inadvertently ruined by leading them astray with his own greedy beliefs. Could they have been like Din once, good people who were made to believe money was more important than family or love?
Fridge Logic
It serves the story with regards to Long's character development showing that he is willing to make a Heroic Sacrifice. However, it seems odd that a powerful wish dragon that we've seen frequently shapeshifting could not somehow magically alter the effects of the Midas Touch on his body to prevent fully turning to gold from being fatal.
It seems lucky that Din was Long's final master. The conditions of his imprisonment were that he was to "serve ten masters AND learn the true meaning of life." Long implies that he breezed through his first nine masters by providing superficial rewards like wealth. Had Din been the same as the others, Long would have fulfilled his 10 master quota but never learned anything and likely would have returned to Heaven only to be found wanting. At that point, having wasted his "second chance," it seems unlikely that he would have been admitted to Heaven.
It's probably no coincidence that the god presiding over Long's spirit made sure to personally hand out his lamp to somebody "pure of heart" for his final master, to avoid exactly this scenario.
If Din ever finds himself in desperate need of money, he knows there's a solid gold dragon and van at the bottom of the river very near the bridge he and Pockets fought on.
