You're forgetting the likely Yuri Milner $150k convertible note, which changes the math somewhat. (If not, we have a "typical case" $14k investment --- n is the number of founders --- for at best 2% post, giving a post valuation of 50*$14k = $700k, which is a very raw deal under the circumstances.)
As to whether this is worth it --- depends on the expenses (which presumably include at least salaries, promotion, and rent). If they aren't spending as much money as they're taking in (no names, but I do know of iPhone devs in this position), it's hard to see the point of giving up equity to get more.
Then again, I think you could consider applying to YC. Even though your revenue > expenses. Don't think of YC as an incubator or a funding machine (or whatever you'd like to call it). They offer a lot more. I think it's more like a ticket to a community of entrepeneurs and investors, based in Silicon Valley.
And yes, the $150k is a nice addition, but would you pick this convertible debt over the weekly dinners, office hours, alumni help you might get and most of all connections with possible investors? I wouldn't :)
Now I think about it: the YC FAQ also mentions this money-related question.
As to whether this is worth it --- depends on the expenses (which presumably include at least salaries, promotion, and rent). If they aren't spending as much money as they're taking in (no names, but I do know of iPhone devs in this position), it's hard to see the point of giving up equity to get more.