Unless you're trying to make a really tight connection or have absolutely no patience for lines, I don't think the $300 per way is worth it. Certainly not on the way out of the country when the lines are minimal. Into the country, if a number of flights get in at one time, the lines can back up. There used to be a lot of pushing and jockeying for position in front of the numerous counters, but they've recently introduced the serpentine lines that mean that everyone gets in one line. This has reduced the ability to cut or push your way to the front, and was a lot more pleasant. It's never taken me more than 15-20 minutes to get through, and that's on a bad day.

There are first class lounges at the airport, but no first class customs queue. Sometimes first class passengers are pulled from plane on separate car instead of bus, which means you would get to the lines before the rest of the passengers (if no jet bridge), but you still could be competing with those who came in on other flights.