My guess on the meaning is that it's about the band trying to keep from being consumed as a fad as their popularity increased. The were at the head of a new musical wave, didn't want to be marketed and used up by music industry types that didn't understand what they were. It's mocking those running from music fad to music fad. But perhaps they are also saying it was inevitable their new music would get crushed, it was born to be burned. Or maybe they were saying it was just the fads that were born to be burned, implying they were immune themselves.

My guess on the meaning is that it's about people with souls crushed by society, lurching through life but can't feel the beauty of it, and miss it all. So their smiles are always dark because they can't really feel pleasure. So what does it matter how far they go on, when life is over, it's just emptiness spilling from the jar (one's being). A caustic comment on straight society. The vacuum leaving the jar is a strikingly powerful metaphor. On another level, this song may also be about making love in the dark to someone she no longer feels passion for, nor does he for her. So what does it matter how far the relationship goes, if it ends, it'd just be a vacuum leaving the jar (the relationship). Darkly smiling may refer to just going through the motions.