Re F over J.. there aren't many flights left that are under 10 hours (LHR-DXB v.v. come to mind) and sure, J would be fine for those 6-7 hour flights, but for your flights to LAX or DFW (or MEL/SYD-DXB through to LHR) the value of F is increased.
For me it's the flat bed WITH aisle access. J is fine, but if you're stuck in the window, getting over someone to get out etc is a PITA. the suite with the bedding, duvet etc are so comfy and obviously far more private, quieter, and the service far more personal.
I'd do it any time I had the chance for that alone. For me it is about comfort and ability to sleep plus ease of access above all else.. The catering is a bit better (well if the load LGD it's a *LOT* better
) and service more personal for sure.
So I think most would see the value in upgrading J-F if they can, specially if points are not so much an issue it would be a no brainer.