

FWIW, the honmoon isn’t powered by music. It’s powered by the consciousness/mood of the populace, which is influenced with music. The demons are trying to steal souls so they can attack it directly. Ostensibly, what they’ve been trying before — such as terrorist attacks on planes as shown in the beginning — hasn’t been as effective. So they’re trying something else.
It’s supposed to be about how music brings people together.
Now, how the demons take souls by getting people to listen to this other band… that’s not as clear. I’d think Soda Pop bringing people together would have the exact same effect on the honmoon as Golden bringing people together, but what do I know?
Smiley Face was made by Greg Araki, who has made some really dark, depressing, and generally fucked-up shit. I mean, he has a movie called “Totally Fucked Up.” If not Smiley Face, he may be best known for The Doom Generation. He also made a few movies with James Duval, who was the crop duster’s son in Independence Day (his first big film IIRC) and Frank the Bunny in Donnie Darko.
Araki made Smiley Face because his last few movies were so depressing, so he wanted to do something a little brighter. That’s why it has “basically no plot,” it’s a feel-good (ish?) movie.