If the AA's F-class has the new sleeper seats, by all means go for the upgrade. What's 20K? As a domestic economy ticket the best it's worth a $199 trip on which you have to make a Saturday night stay before returning. While it's not Singapore or Cathay Pacific, the physical amenities will cover off any of AA's difficiencies in service. And you'll also get to experience AA's new Flagship lounge if there's one at your gateway airport.
Go for it. And of course, let us know after you've done it, what you think.