Really enjoyed reading your report, Brit.
I too have found the AA J headrests uncomfortable, but every time I have flown AA J, it has been as a result of an operational upgrade so I'm not complaining!
And I too find the LHR Admirals' Club too crowded. I always use the BA Business lounge (also by gate 12 but on the other side of the corridor). You have access to it as AA PLT. There have never been more than 10 people there when I have used as BA has only 1 flight leaving for MIA inthe afternoon I think. The food selection is much better and you can stock up on some packeted snacks/ cake for the flight.