I watched a video of the ride and it seems a little boring. Is it worth the hassle or a Fastpass?
Given that you have to choose between Navi or Flights of Passage, I'd choose FoP if at all possible.
If FoP isn't available, then pick Navi.
Navi is a slow boat ride. It's very pretty, and if you enjoy that sort of thing, you'll like it very much. I loved it, personally. But, you know, I also love Living with the Land over in Epcot.
If there are other rides you'd rather go on, then try to get Navi as your fourth fastpass, or hop in line for it about 10 minutes before park close. I don't think any ride is worth waiting more than 30 minutes in line for, but at park close the estimated wait times tend to be inflated. With no fastpass returns coming in, the line will move quickly.
You should try to ride it at least once.
YouTube videos can make almost anything look awful. You won't know if you really like it, until you try it.