I bought a NW WC lifetime membership 10 or 12 years ago. My wife, who is the CFO in our business asked me at the time if I could plan on living 15 more years so we could make it break even. Of course, prices have gone up so we've more then made the breakeven point. Even if it's $3700, it is still a good deal if you're going to fly for a while.
I'm 50, and god willing, hopefully I'm good for another 25 years or so.