Well, with a week before nationals, I bet what I'll say won't do much for you one way or another, buuuut take it for what it's worth:
Having been in that situation more than once, I'd say that you should just do what lines up most with what you want out of things.
At Nats '07, I really wanted to earn the Hawaii trip...But I also wanted to win Nationals. So what did I do? Play until I felt like I had a real chance of losing the trip.
At Nats '08, since there was no trip attached to the invite, I decided that dropping or sitting out on an opportunity at winning five grand, some decently-neat prizes, and eternal Pokeyman glory was worth more.
So...Given how "risky" your ranking is right now, I'd say that you might find this to be a very bad ex post mistake. However, if you get the invite, then you'll do what you've been wanting to do for over five years: get a worlds invite.
All I have to say beyond that is "good luck," because I'll probably take your invite by shooting up in the rankings after I win.