We've had a couple of big BBJ winners on this site. If you can play and table select well enough to beat the jackpot rake, then yes, they're worthwhile. The jackpots hit most often at $50 NL because there are more
hands dealt there, but payouts are bigger when it hits at other levels because fewer players split them.
In my experience, the best time to play is at off-peak hours (after midnight Pacific time) and when the jackpot is high (between $200-$300k) but not super high. That way you'll get paid decently if it hits. When the jackpot is huge it attracts craploads of players, and your best hope of making money is taking advantage of those who are only thinking about the jackpot and playing suboptimally because of it.
If you're multitabling when it hits you'll thank yourself, but don't lose a bunch chasing a jackpot because it's a long shot.