The vague Tarot symbolism is Japanese in a way that's not quite as cool. I keep seeing this technique where they'll bring up a theme or a set of symbols (angels, Catholicism, the moon, etc.) and then not really pursue them. If everyone on TeamFightGiantMonster wears a big silver cross on a chain, it's never explained, and they don't act as they would if the big silver crosses meant anything.
The Tarot symbolism in Persona 3 is actually fairly functional in mythic/symbolic/whatever terms. Essentially, your supernatural ability is a "persona": a mythical figure or creature that corresponds to the face you put on to the world, which you're able to physically manifest under certain circumstances. Due to Reasons, your main character is able to change his Persona relatively easily, but the strength of a given Persona generally corresponds to how much you've developed that face of yourself. Each Persona corresponds to one of the major arcana of the tarot, some in obvious ways (Apollo is Sun, Pale Rider is Death, most angels are Justice) and some in nonobvious ways. Each of the characters you can create a social link with also corresponds to one of the major arcana, and although it's sometimes in ways that aren't immediately obvious, the connection becomes clear as you become closer to them. The more you develop a social link, the stronger the Personae of that arcana will be.
So, yeah, it's not really throwaway symbolism. The series creator is a big fan of Jung, and while it's not as all-pervading in this as in the earlier games, it does inform the game's construction.
Reflecting on it, I think one of the things I like best about this game is that it is intended to make you uncomfortable - not in a "OH LOOK HOW SHOCKING WE CAN BE" way, but in a quiet way that comes from reflecting on how someone who acts like a video game protagonist would fit into society after playing without noticing for long enough. A number of the social links will grow faster if you essentially act as an enabler to unhealthy behavior - from a typical video-gaming perspective, this is the "right way to play" but after a while it might grow on you that maybe it's not really the best thing to do.